<PAGE>   1
================================================================================

                UNITED STATES SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                    FORM 10-K

  |X|    ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES 
-------  EXCHANGE ACT OF 1934

FOR THE FISCAL YEAR ENDED:  DECEMBER 31, 1998

                                       OR

         TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
-------  EXCHANGE ACT OF 1934

FOR THE TRANSITION PERIOD FROM ____________ TO ______________

COMMISSION FILE NUMBER:  33-47912

                          CMC SECURITIES CORPORATION IV
             (Exact name of Registrant as specified in its Charter)

              DELAWARE                                       75-2431915
   (State or other jurisdiction of                        (I.R.S. Employer
    incorporation or organization)                       Identification No.)

       2711 NORTH HASKELL AVENUE                                 75204
(Address of principal executive offices)                       (Zip Code)

       Registrant's telephone number, including area code: (214) 874-2323

        Securities registered pursuant to Section 12(b) of the Act: None.

        Securities registered pursuant to Section 12(g) of the Act: None.

Indicate by check mark whether the Registrant (1) has filed all documents and
reports required to be filed by Section 13 or 15(d) of the Securities Exchange
Act of 1934 during the preceding 12 months (or for such shorter period that the
Registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. YES   |X|   NO
                                              ------     ------

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
Regulation S-K is not contained herein, and will not be contained, to the best
of Registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K |_|

At March 31, 1999 the aggregate market value of the voting stock held by
nonaffiliates was: Not Applicable.

The Registrant meets the conditions set forth in General Instruction J(1)(a)
and (b) of Form 10-K and is, therefore, filing this Form with reduced disclosure
format.

Number of shares of Common Stock outstanding at March 25, 1999:  1,000

                   DOCUMENTS INCORPORATED BY REFERENCE: None.

================================================================================

<PAGE>   2

                          CMC SECURITIES CORPORATION IV

                          1998 FORM 10-K ANNUAL REPORT

                                TABLE OF CONTENTS




<TABLE>
<CAPTION>
                                                                                              PAGE
                                                                                              ----
<S>          <C>                                                                              <C>

                                     PART I

ITEM  1.      BUSINESS..................................................                        1

ITEM  2.      PROPERTIES................................................                        3

ITEM  3.      LEGAL PROCEEDINGS.........................................                        3


                                     PART II

ITEM  5.      MARKET FOR THE REGISTRANT'S COMMON EQUITY
                 AND RELATED STOCKHOLDER MATTERS.........................                       3

ITEM  7.      MANAGEMENT'S DISCUSSION AND ANALYSIS OF
                 FINANCIAL CONDITION AND RESULTS OF OPERATIONS...........                       3

ITEM  8.      FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA...............                        4

ITEM  9.      CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON
                 ACCOUNTING AND FINANCIAL DISCLOSURE.....................                      15


                                     PART IV

ITEM 14.      EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND
                 REPORTS ON FORM 8-K.....................................                      16
</TABLE>


<PAGE>   3


                                     PART I

ITEM 1.  BUSINESS.

ORGANIZATION

CMC Securities Corporation IV (the "Company") was incorporated in Delaware on
May 6, 1992, as a special-purpose finance corporation and is a wholly-owned
subsidiary of Capstead Mortgage Corporation ("CMC"). CMC is a publicly-owned
real estate investment trust that, until late 1995, operated as a mortgage
conduit, purchasing and securitizing single-family residential mortgage loans.
The Company is managed by CMC (the "Manager").

Due to changing circumstances, control of the Company within CMC's consolidated
group was changed twice during 1994 and 1995. In August 1994, CMC sold all the
issued and outstanding shares of capital stock in the Company to Capstead Inc.,
CMC's subsidiary formed primarily to service single-family mortgage loans. On
December 21, 1995, after CMC reached a decision to exit the mortgage conduit
business, the Company was merged with and into a newly formed and wholly-owned
subsidiary of CMC (with a corporate charter and organizational structure
identical in almost all respects to that of the Company) ("CMCSC IV-A") whereby
the existence of the Company ceased and CMCSC IV-A acquired all the assets and
assumed all the liabilities of the Company as the surviving entity. As merger
consideration to Capstead Inc., CMCSC IV-A paid an amount of $430,000 in cash
that had been contributed by CMC. As a part of the merger, CMCSC IV-A changed
its name to CMC Securities Corporation IV, and from December 21, 1995 forward
has been referred to as the "Company."

The Company was formed primarily for the purpose of issuing collateralized
mortgage obligations ("Bonds" or "CMOs"), collateralized by mortgage-backed,
pass-through certificates ("Certificates") that evidence an interest in a pool
of mortgage loans secured by single-family residences. The Certificates pledged
as collateral for the Bonds will either be contributed by CMC or its affiliates
or purchased from third parties and will either be Government National Mortgage
Association certificates, Federal National Mortgage Association certificates,
Federal Home Loan Mortgage Corporation certificates or mortgage pass-through
("Non-Agency") Certificates. The Company's Certificate of Incorporation requires
that Bonds issued be rated in one of the two highest rating categories
established by one or more nationally recognized statistical rating agencies.

On August 17, 1992 the Securities and Exchange Commission declared effective an
amended registration statement filed by the Company covering the offering of a
maximum of $2 billion aggregate principal amount of CMOs. The Company commenced
operations with the September 30, 1994 issuance of its first series of CMOs. The
Company did not issue any CMOs during 1996 or 1995. During 1997 the Company
issued two series of CMOs (Series 1997-NAMC 3 and 1997-2) with total obligations
(including accrued interest and premium) of $1.2 billion. The Company retained
no beneficial interest in these CMOs, and as such, no economic benefit will be
received and no related net income or loss will be recognized other than the
amortization of unrecovered shelf issuance costs. These issuances were accounted
for as financings. As of December 31, 1998, the Company had issued 5 series of
CMOs with an aggregate original principal balance of $2,003,125,000,
$176,304,000 of which were issued outside the registration statement as private
placements.


                                      -1-
<PAGE>   4

SPECIAL-PURPOSE FINANCE CORPORATION

The Company has not engaged and will not engage in any business or investment
activities other than (i) issuing and selling CMOs, and receiving, owning,
holding and pledging as collateral the related Certificates, (ii) investing cash
balances on an interim basis in high quality short-term securities, and (iii)
engaging in other activities which are necessary or convenient to accomplish the
foregoing and are incidental thereto. Article III of the Company's Certificate
of Incorporation limits the Company's purposes to the above.

COMPETITION

The Company's business is highly competitive. The Company competes with other
issuers of similar obligations, both with respect to the acquisition of mortgage
related collateral, securing the Bonds and the placement of the CMOs. The
Company also competes with entities that issue and/or market numerous other
competitive financial products.

EMPLOYEES

At December 31, 1998 the Company had no employees. The Manager provides all
executive and administrative personnel required by the Company.

MANAGEMENT AGREEMENT

Pursuant to a management agreement, the Manager advises the Company with respect
to its investments and administers the day-to-day operations of the Company. The
management agreement is nonassignable except by consent of the Company and the
Manager. The management agreement may be terminated without cause at any time
upon 90 days written notice. In addition, the Company has the right to terminate
the management agreement upon the happening of certain specified events,
including a breach by the Manager of any provision contained in the management
agreement which remains uncured for 30 days after notice of such breach and the
bankruptcy or insolvency of the Manager.

The Manager is at all times subject to the supervision of the Company's Board of
Directors and has only such functions and authority as the Company delegates to
it. The Manager is responsible for the day-to-day operations of the Company and
performs such services and activities relating to the assets and operations of
the Company as may be appropriate. The Manager receives an annual basic
management fee of $10,000 per year for managing the assets pledged to secure
Bonds issued by the Company.

The Manager is required to pay employment expenses of its personnel (including
salaries, wages, payroll taxes, insurance, fidelity bonds, temporary help and
costs of employee benefit plans), and other office expenses, travel and other
expenses of directors, officers and employees of the Manager, accounting fees
and expenses incurred in supervising and monitoring the Company's investments or
relating to performance by the Manager of its functions. The Company is required
to pay all other expenses of operation (as defined in the management agreement).

SERVICING AND ADMINISTRATION

The originators of mortgage loans backing the Non-Agency Certificates may elect,
if they meet the Company's criteria for servicers, either to service


                                      -2-
<PAGE>   5

the loans they sell or to sell the loans with no agreement with respect to
servicing. The Company enters into servicing agreements with each servicer.

As compensation for services rendered under the servicing agreements, the
servicers retain a servicing fee, payable monthly, generally 1/4 of 1% per annum
of the outstanding principal balance of each mortgage loan serviced as of the
last day of each month. During 1998 Capstead Inc. serviced a significant number
of the Company's mortgage loans. This servicing was sold by Capstead Inc. in
December 1998 to an unaffiliated third party. During 1998, 1997 and 1996,
Capstead Inc. retained fees from mortgage loan payments for servicing mortgage
loans of $940,000, $1,174,000 and $1,225,000, respectively.

In addition, CMC acts as administrator with respect to certain of the Company's
Non-Agency Certificates and CMOs. During 1998, 1997 and 1996, CMC retained fees
for administering the Non-Agency Certificates and CMOs of $253,000, $297,000 and
$341,000, respectively.

ITEM 2.   PROPERTIES.

The Company's operations will be conducted primarily in Dallas, Texas on
properties leased by CMC.

ITEM 3.   LEGAL PROCEEDINGS.

As of the date hereof, there are no material legal proceedings outside the
normal course of business to which the Company was a party or of which any of
its property was the subject.

                                     PART II


ITEM 5.   MARKET FOR THE REGISTRANT'S COMMON EQUITY AND RELATED STOCKHOLDER
          MATTERS.

All of the Company's common stock is owned by CMC. Accordingly, there is no
public trading market for its common stock. To date the Company has not paid
dividends.

ITEM 7.  MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
         OF OPERATIONS.

The Company commenced operations on September 30, 1994 with the issuance of its
first series of CMOs. Two additional series of CMOs were issued in both 1994 and
1997. The Company elected Real Estate Mortgage Investment Conduit ("REMIC")
status for tax purposes on these transactions. These issuances have been
accounted for as financings. As financings, CMO collateral and Bonds are
reflected on the balance sheet.

Since the Company did not retain any investment in the CMOs issued, no economic
benefit was or will be received and thus no net income or loss was or will be
recognized related to these CMOs other than amortization of unreimbursed shelf
issuance costs. The Company's net losses are due to this amortization and
operational costs incurred (management fees and professional fees).


                                      -3-
<PAGE>   6



LIQUIDITY AND CAPITAL RESOURCES

All ongoing cash CMO expenses are paid out of the excess cash flows on the CMOs
issued before the residual holders receive their residual interest. The Company
believes that the excess cash flows will be sufficient to pay ongoing cash CMO
expenses. Cash flow requirements due to ongoing operational costs are funded by
CMC.

IMPACT OF YEAR 2000

Many existing computer software programs use only two digits to identify the
year in date fields and, as such, could fail or create erroneous results by or
at the Year 2000. The Manager utilizes a number of software systems to
administer securitizations and otherwise manage the Company's affairs. In
addition, the Manager utilizes vendors in various capacities and interfaces with
various institutions. The Manager is exposed to the risk that its systems and
the systems of its vendors and institutions it interfaces with are not Year 2000
compliant.

     State of Readiness. The Manager has made and will continue to make
investments in its software systems and applications to ensure the Manager is
Year 2000 compliant. The Manager is also taking steps to ensure that the vendors
it utilizes and institutions that it interfaces with are also taking the
necessary steps to become Year 2000 compliant. This process is expected to be
essentially complete by the end of the second quarter of 1999.

     Costs. The financial costs of the Manager becoming Year 2000 compliant is
the responsibility of the Manager.

     Risks and Contingency Planning. Although the Manager expects that all its
systems and applications will be Year 2000 compliant per the above schedule and
well prior to December 31, 1999, there can be no assurance that all of the
vendors it utilizes and institutions that it interfaces with will complete their
compliance efforts. The Manager will continue to monitor their efforts in this
regard and will take all prudent steps necessary to ensure operations are not
disrupted including the use of other vendors or other methodologies and
processes to transact the Company's business. The effect of any disruption to
the Company's operations of any such instances of non-compliance is presently
not determinable.


ITEM 8.   FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA.


                                      -4-
<PAGE>   7



                           REPORT OF ERNST & YOUNG LLP
                              INDEPENDENT AUDITORS



Stockholder and Board of Directors
CMC Securities Corporation IV

We have audited the accompanying balance sheet of CMC Securities Corporation IV
(a wholly-owned subsidiary of Capstead Mortgage Corporation) as of December 31,
1998 and 1997, and related statements of operations, stockholder's equity, and
cash flows for each of the three years in the period ended December 31, 1998.
These financial statements are the responsibility of the Company's management.
Our responsibility is to express an opinion on these financial statements based
on our audits.

We conducted our audits in accordance with generally accepted auditing
standards. Those standards require that we plan and perform the audit to obtain
reasonable assurance about whether the financial statements are free of material
misstatement. An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements. An audit also includes
assessing the accounting principles used and significant estimates made by
management, as well as evaluating the overall financial statement presentation.
We believe that our audits provide a reasonable basis for our opinion.

In our opinion, the financial statements referred to above present fairly, in
all material respects, the financial position of CMC Securities Corporation IV
at December 31, 1998 and 1997, and the results of its operations and its cash
flows for each of the three years in the period ended December 31, 1998, in
conformity with generally accepted accounting principles.





Dallas, Texas
February 4, 1999



                                      -5-
<PAGE>   8



                          CMC SECURITIES CORPORATION IV
                                  BALANCE SHEET
                      (IN THOUSANDS, EXCEPT PER SHARE DATA)



<TABLE>
<CAPTION>
                                                                         DECEMBER 31        
                                                             ------------------------------------
                                                                1998                      1997   
                                                             ----------                ----------
<S>                                                          <C>                       <C>
ASSETS
   Mortgage securities collateral                            $1,171,151                $1,728,030
   Cash and cash equivalents                                          1                         2
                                                             ----------                ----------

                                                             $1,171,152                $1,728,032
                                                             ==========                ==========

LIABILITIES
   Collateralized mortgage securities                        $1,171,031                $1,727,766
   Accrued expenses                                                  42                        32
                                                             ----------                ----------

                                                              1,171,073                 1,727,798
                                                             ----------                ----------

STOCKHOLDER'S EQUITY
   Common stock - $1.00 par value, 1 shares
     authorized, issued and outstanding                               1                         1
   Paid-in capital                                                  432                       490
   Undistributed loss                                              (354)                     (257)
                                                             ----------                ----------

                                                                     79                       234
                                                             ----------                ----------

                                                             $1,171,152                $1,728,032
                                                             ==========                ==========
</TABLE>








See accompanying notes to financial statements.


                                      -6-
<PAGE>   9



                          CMC SECURITIES CORPORATION IV
                             STATEMENT OF OPERATIONS
                                 (IN THOUSANDS)



<TABLE>
<CAPTION>
                                                                      YEAR ENDED DECEMBER 31    
                                                            ----------------------------------------
                                                              1998             1997           1996  
                                                            --------          -------        -------
<S>                                                         <C>               <C>            <C>
Interest income on
   mortgage securities collateral                           $115,627          $67,475        $55,193

Interest expense on collateralized
   mortgage securities                                       115,697           67,563         55,281
                                                            --------          -------        -------

       Net interest expense                                      (70)             (88)           (88)
                                                            --------          -------        -------

Other expenses:
   Management fees                                                10               10             10
   Professional fees and other                                    17               14             15
                                                            --------          -------        -------

     Total other expenses                                         27               24             25
                                                            --------          -------        -------

Net loss                                                    $    (97)         $  (112)       $  (113)
                                                            ========          =======        =======
</TABLE>






See accompanying notes to financial statements.


                                      -7-
<PAGE>   10



                          CMC SECURITIES CORPORATION IV
                        STATEMENT OF STOCKHOLDER'S EQUITY
                       THREE YEARS ENDED DECEMBER 31, 1998
                                 (IN THOUSANDS)



<TABLE>
<CAPTION>
                                           COMMON STOCK           PAID-IN            UNDISTRIBUTED
                                       SHARES     AMOUNT          CAPITAL            INCOME (LOSS)         TOTAL
                                       ------     ------          -------            -------------         -----
<S>                                    <C>        <C>             <C>                <C>                   <C>
Balance at
   January 1, 1996                      1          $1             $461                  $(32)              $ 430

Capital contribution                    -           -               13                     -                  13

Net loss                                -           -                -                  (113)               (113)
                                        -          --             ----                 -----               -----

Balance at
   December 31, 1996                    1           1              474                  (145)                330

Capital contribution                    -           -               16                     -                  16

Net loss                                -           -                -                  (112)               (112)
                                        -          --             ----                 -----               -----

Balance at
   December 31, 1997                    1           1              490                  (257)                234

Capital distribution                    -           -              (58)                    -                 (58)

Net loss                                -           -                -                   (97)                (97)
                                        -          --             ----                 -----               -----

Balance at
   December 31, 1998                    1          $1             $432                 $(354)              $  79
                                        =          ==             ====                 =====               =====
</TABLE>






See accompanying notes to financial statements.


                                      -8-
<PAGE>   11



                          CMC SECURITIES CORPORATION IV
                             STATEMENT OF CASH FLOWS
                                 (IN THOUSANDS)



<TABLE>
<CAPTION>
                                                                             YEAR ENDED DECEMBER 31      
                                                                 -----------------------------------------------
                                                                   1998                1997               1996  
                                                                 --------           -----------         --------
<S>                                                             <C>                 <C>                 <C>
OPERATING ACTIVITIES:
   Net loss                                                      $    (97)          $      (112)        $   (113)
   Noncash item - amortization
     of discount and premium                                           19                    61               66
   Net change in other assets and
     accrued expenses                                                  10                    10               10
                                                                 --------           -----------         --------
         Net cash used by
           operating activities                                       (68)                  (41)             (37)
                                                                 --------           -----------         --------

INVESTING ACTIVITIES:
   Mortgage securities collateral:
     Mortgage collateral acquired
       from affiliate                                                   -            (1,187,085)               -
     Principal collections on collateral                          559,522                81,555           77,716
     Decrease (increase) in accrued
       interest receivable                                          3,745                (7,060)             484
     Increase in short-term investments                                 -                    (2)              (7)
                                                                ---------           -----------         --------
         Net cash provided (used) by
           investing activities                                   563,267            (1,112,592)          78,193
                                                                ---------           -----------         --------

FINANCING ACTIVITIES:
   Collateralized mortgage securities:
     Issuance of securities                                             -             1,187,085                -
     Principal payments on securities                            (559,522)              (81,555)         (77,716)
     Increase (decrease) in accrued
       interest payable                                            (3,620)                7,089             (455)
   Capital contribution (distribution)                                (58)                   16               13
                                                                ---------           -----------         --------
         Net cash provided (used) by
           financing activities                                  (563,200)            1,112,635          (78,158)
                                                                ---------           -----------         --------

Net change in cash and cash equivalents                                (1)                    2               (2)

Cash and cash equivalents at
   beginning of year                                                    2                     -                2
                                                                ---------           -----------         --------

Cash and cash equivalents at end
     of year                                                    $       1           $         2         $      -
                                                                =========           ===========         ========
</TABLE>



See accompanying notes to financial statements.


                                      -9-
<PAGE>   12



                          CMC SECURITIES CORPORATION IV
                          NOTES TO FINANCIAL STATEMENTS
                                DECEMBER 31, 1998



NOTE A -- BUSINESS

CMC Securities Corporation IV (the "Company") was incorporated in Delaware on
May 6, 1992, as a special-purpose finance corporation primarily to issue bonds
collateralized by whole loans or mortgage-backed securities. Capstead Inc.
acquired the Company from Capstead Mortgage Corporation ("CMC"), the then parent
of Capstead Inc., on August 10, 1994 pursuant to a Stock Purchase Agreement
prior to commencement of operations; however, control of the Company was
transferred back to CMC on December 21, 1995 pursuant to an Agreement and Plan
of Merger (see Note G).

NOTE B -- ACCOUNTING POLICIES

USE OF ESTIMATES
----------------

The preparation of the financial statements in conformity with generally
accepted accounting principles requires management to make estimates and
assumptions that affect the amounts reported in the financial statements and
accompanying notes. Actual results could differ from those estimates.

SECURITIES HELD-TO-MATURITY
---------------------------

Management determines the appropriate classification of debt securities at the
time of purchase and reevaluates such designation as of each balance sheet date.
Debt securities are classified as held-to-maturity when the Company has the
positive intent and ability to hold the securities to maturity. Held-to-maturity
securities are stated at amortized cost.

MORTGAGE SECURITIES COLLATERAL
------------------------------

Mortgage securities collateral consists of debt securities classified as
held-to-maturity. Amortized cost is adjusted for amortization of premiums and
discounts over the estimated life of the security using the interest method.
Such amortization is included in related interest income.

Mortgage securities collateral is subject to changes in value because of changes
in interest rates and rates of prepayment, as well as failure of the mortgagor
to perform under the mortgage agreement. The Company has limited its exposure to
these risks by issuing collateralized mortgage securities, using a
senior/subordinate structure (see Note F).

ALLOWANCE FOR POSSIBLE LOSSES
-----------------------------

The Company provides for possible losses on its investments in amounts which it
believes are adequate relative to the risk inherent in such investments.

COLLATERALIZED MORTGAGE SECURITIES
----------------------------------

Collateralized mortgage securities are carried at their unpaid principal
balances, net of unamortized discount or premium. Any discount or premium is

                                      -10-
<PAGE>   13



recognized as an adjustment to interest expense by the interest method over the
life of the related securities.

INCOME TAXES
------------

Since its inception through August 9, 1994, the Company operated as a qualified
real estate investment trust ("REIT") subsidiary of CMC, which itself is a REIT,
and was combined with CMC for federal income tax purposes. REITs are not taxed
at the corporate level provided that certain requirements are met. From August
10, 1994 through December 21, 1995 the Company was consolidated for income tax
purposes with Capstead Inc., which is not a REIT; however, due to losses
incurred during this period, no provision was made for federal income taxes.
Beginning December 21, 1995 the Company once again began operating as a
qualified REIT subsidiary of CMC.

CASH AND CASH EQUIVALENTS
-------------------------

Cash and cash equivalents include cash on hand and highly liquid investments
with original maturities of three months or less.

NOTE C -- MORTGAGE SECURITIES COLLATERAL

Mortgage securities collateral consists of conventional single-family mortgage
loans which are pledged to secure repayment of the collateralized mortgage
securities. All principal and interest payments on the collateral are remitted
directly to a collection account maintained by a trustee. The trustee is
responsible for reinvesting those funds in short-term investments. All
collections on the collateral and the reinvestment income earned thereon are
available for payment of principal and interest on the collateralized mortgage
securities. The components of mortgage securities collateral are summarized as
follows (in thousands):

<TABLE>
<CAPTION>
                                                                                    DECEMBER 31     
                                                                       -----------------------------------
                                                                          1998                      1997  
                                                                       ----------               ----------
<S>                                                                    <C>                      <C>
 
         Mortgage collateral                                           $1,190,070               $1,749,592
         Short-term investments                                                 9                        9
         Accrued interest receivable                                        7,200                   10,945
                                                                       ----------               ----------
           Total collateral                                             1,197,279                1,760,546
         Unamortized discount                                             (26,128)                 (32,516)
                                                                       ----------               ----------

         Net collateral                                                $1,171,151               $1,728,030
                                                                       ==========               ==========
</TABLE>

The weighted average effective interest rate for mortgage securities collateral
was 7.92% and 8.65% during 1998 and 1997, respectively.

NOTE D -- COLLATERALIZED MORTGAGE SECURITIES

Each series of collateralized mortgage securities consists of various classes,
some of which may be deferred interest, interest-only and principal-only
securities. Interest is payable monthly at specified rates for all classes other
than deferred interest securities. Generally, principal payments on each series
are made to each class in the order of their stated maturities so that no
payment of principal will be made on any class until all classes having an
earlier stated maturity have been paid in full. Generally, payments of principal
and interest on deferred interest securities will commence only upon payment in
full of some or all other classes. Prior


                                      -11-
<PAGE>   14

to that time, interest accrues on the deferred interest securities and the
amount accrued is added to the unpaid principal balance. Interest payments on
interest-only bonds are based on a specified notional amount used only for the
calculation of interest and no payments of principal are made. Principal-only
bonds remit principal payments and no interest is paid.

The components of collateralized mortgage securities are summarized as follows
(dollars in thousands):

<TABLE>
<CAPTION>
                                                                                      DECEMBER 31         
                                                                         ------------------------------------
                                                                            1998                      1997   
                                                                         ----------                ----------
<S>                                                                      <C>                       <C> 
   Collateralized mortgage securities                                    $1,190,070                $1,749,592
   Accrued interest payable                                                   7,107                    10,801
                                                                         ----------                ----------
     Total obligation                                                     1,197,177                 1,760,393
   Unamortized discount                                                     (26,146)                  (32,627)
                                                                         ----------                ----------

   Net obligation                                                        $1,171,031                $1,727,766
                                                                         ==========                ==========

   Range of average interest rate                                      6.36% to 8.26%            6.36% to 8.16%
   Stated maturities                                                    2024 to 2027              2024 to 2027
   Number of series                                                           5                         5 
</TABLE>


The maturity of each series of securities is directly affected by the rate of
principal prepayments on the related mortgage securities collateral. Each series
of securities is also subject to redemption at the Company's option provided
that certain requirements specified in the related indenture have been met
(referred to as "clean-up calls"). As a result, the actual maturity of any
series of securities is likely to occur earlier than its stated maturity.

The weighted average effective interest rate for collateralized mortgage
securities was 7.93% and 8.66% during 1998 and 1997, respectively. Interest
payments on collateralized mortgage securities of $110,882,000, $52,621,000 and
$47,853,000 were made during 1998, 1997 and 1996, respectively.

NOTE E -- DISCLOSURES REGARDING FAIR VALUES OF FINANCIAL INSTRUMENTS

The estimated fair value of financial instruments have been determined by the
Company using available market information and appropriate valuation
methodologies; however, considerable judgment is required in interpreting market
data to develop these estimates. In addition, fair values fluctuate on a daily
basis. Accordingly, the estimates presented herein are not necessarily
indicative of the amounts that the Company could realize in a current market
exchange. The use of different market assumptions and/or estimation
methodologies may have a material effect on the estimated fair value amounts.

The carrying amount of cash and cash equivalents approximates fair value. The
fair value of mortgage securities collateral was estimated using either quoted
market prices, when available, including quotes made by CMC's lenders in
connection with designating collateral for repurchase arrangements. The fair
value of collateralized mortgage securities is dependent upon the
characteristics of the mortgage securities collateral pledged to secure the
issuance. Therefore, fair value was based on the same method used for
determining fair value for the underlying mortgage securities collateral,
adjusted for credit enhancements.


                                      -12-
<PAGE>   15



The following table summarizes the fair value of financial instruments (in
thousands):

<TABLE>
<CAPTION>
                                                    DECEMBER 31, 1998                 DECEMBER 31, 1997
                                              ---------------------------        --------------------------
                                              CARRYING           FAIR             CARRYING         FAIR
                                               AMOUNT            VALUE             AMOUNT          VALUE
                                              ----------       ----------        ----------      ----------
<S>                                           <C>              <C>               <C>             <C>
ASSETS
   Cash and cash equivalents                  $        1       $        1        $        2      $        2
   Mortgage securities collateral              1,171,151        1,220,545         1,728,030       1,791,145

LIABILITIES
   Collateralized mortgage
     securities                                1,171,031        1,226,691         1,727,766       1,807,150
</TABLE>

The table above reflects the estimated fair value of mortgage securities
collateral and cash equivalents as of December 31, 1998 and 1997, which reflect
gross unrealized gains of $49.4 million and $63.1 million, respectively.

NOTE F -- ALLOWANCE FOR POSSIBLE LOSSES

The Company has limited exposure to losses on mortgage securities collateral
because the Company's collateralized mortgage securities are issued in a
senior/subordinate structure where the investor in the subordinate classes
assumes the risks of losses due to typical mortgagor default and special
hazards. Special hazards are typically catastrophic events that are unable to be
predicted (e.g., earthquakes). Because of its limited exposure to losses, the
Company has determined that an allowance for possible losses is not warranted at
December 31, 1998.

Since 25% of mortgage securities collateral is secured by properties located in
California, the Company has a concentration of risk related to the California
market. However, the Company's exposure arising from this concentration is
reduced by the use of the senior/subordinate structure for securitizations.

NOTE G -- CHANGE IN CONTROL

On August 9, 1994, the Company amended its Certificate of Incorporation to
revise certain provisions thereof to meet current rating agency criteria and to
change its name to CMC Securities Corporation IV. Pursuant to a Stock Purchase
Agreement dated August 10, 1994, CMC sold all of the issued and outstanding
shares of capital stock in the Company to Capstead Inc. for $708,000. Such
amount was funded by an advance from CMC to Capstead Inc.
under a revolving credit facility between such companies.

Pursuant to an Agreement and Plan of Merger dated December 21, 1995 (the
"Agreement") between the Company and CMC Securities Corporation IV-A ("CMCSC
IV-A"), a newly formed and wholly-owned subsidiary of CMC with a corporate
charter and organizational structure identical in almost all respects to that of
the Company, the Company merged with and into CMCSC IV-A, whereby the existence
of the Company ceased and CMCSC IV-A acquired all of the assets and assumed all
of the liabilities of the Company as the surviving entity. CMCSC IV-A paid
Capstead Inc. $430,000 as merger consideration that


                                      -13-
<PAGE>   16

had been contributed to CMCSC IV-A by CMC. As a part of the merger, CMCSC IV-A
changed its name to CMC Securities Corporation IV.

NOTE H -- MANAGEMENT AGREEMENT

The Company operates under a $10,000 per year management agreement with CMC (the
"Manager"). The agreement provides that the Manager will advise the Company with
respect to all facets of its business and administer the day-to-day operations
of the Company under the supervision of the Company's Board of Directors. The
Manager pays among other things, salaries and benefits of its personnel,
accounting fees and expenses, and other office expenses incurred in supervising
and monitoring the Company's investments.

NOTE I -- TRANSACTIONS WITH RELATED PARTIES

The Company has entered into servicing agreements with Capstead Inc., the
provisions of which are typical of such agreements in the mortgage servicing
industry. Capstead Inc. sold this servicing to an unaffiliated third party in
December 1998. Under the servicing agreements, Capstead Inc. retained from
interest collected a servicing fee generally 1/4 of 1% per annum of the
outstanding principal balance of mortgage loans serviced. Servicing fees of
$940,000, $1,174,000 and $1,225,000 were retained by Capstead Inc. in 1998, 1997
and 1996, respectively.

CMC acts as administrator in relation to certain of the Company's Non-Agency
Certificates and CMOs in which it performs certain administrative functions. CMC
receives fees of approximately 0.015% to 0.04% per annum of the outstanding
principal amount of the bonds, after deducting trustee fees. Such fees totaled
$253,000, $297,000 and $341,000 in 1998, 1997 and 1996, respectively.

During 1995 the Company had a $20 million revolving subordinated promissory note
with Capstead Inc. under which interest accrued on amounts payable based on the
annual federal short-term rate as published by the Internal Revenue Service.
This note matured January 1, 1996 and has been replaced with a $1 million note
with CMC that contains similar terms and expires January 1, 2000.

NOTE J -- NET INTEREST INCOME ANALYSIS (UNAUDITED)

The following table summarizes the amount of interest income and interest
expense and the average effective interest rate for mortgage securities
collateral and collateralized mortgage securities (dollars in thousands):

<TABLE>
<CAPTION>
                                               1998                         1997                      1996 
                                       ---------------------        --------------------        -------------------
                                                     AVERAGE                     AVERAGE                    AVERAGE
                                        AMOUNT         RATE          AMOUNT       RATE          AMOUNT        RATE 
                                       --------      -------        -------      -------        -------     -------
<S>                                    <C>           <C>            <C>           <C>           <C>         <C>
Interest income on
   mortgage securities
   collateral                          $115,627       7.92%         $67,475       8.65%         $55,193     8.68%
Interest expense on
   collateralized
   mortgage securities                  115,697       7.93           67,563       8.66           55,281     8.69 
                                       --------                     -------                     -------

Net interest expense                   $    (70)                    $   (88)                    $   (88)
                                       ========                     =======                     =======

</TABLE>


                                      -14-
<PAGE>   17



The following is a summary of the amount of change in interest income and
interest expense due to changes in interest rates versus changes in volume (in
thousands):

<TABLE>
<CAPTION>
                                                                     1998/1997       
                                                     -------------------------------------------
                                                      RATE             VOLUME             TOTAL 
                                                     -------           -------           -------
<S>                                                  <C>               <C>               <C>
Interest income on mortgage
   securities collateral                             $(6,132)          $54,284           $48,152
Interest expense on collateralized
   mortgage securities                                (6,201)           54,335            48,134
                                                     -------           -------           -------

                                                     $    69           $   (51)          $    18
                                                     =======           =======           =======


<CAPTION>
                                                                     1997/1996       
                                                     -------------------------------------------
                                                      RATE             VOLUME             TOTAL 
                                                     -------           -------           -------
<S>                                                  <C>               <C>               <C>
Interest income on mortgage
   securities collateral                             $  (166)          $12,448           $12,282
Interest expense on collateralized
   mortgage securities                                  (191)           12,473            12,282
                                                     -------           -------           -------

                                                     $    25           $   (25)          $     -
                                                     =======           =======           =======
</TABLE>


ITEM 9.   CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND 
          FINANCIAL DISCLOSURE.

None.


                                      -15-
<PAGE>   18



                                     PART IV

ITEM 14.  EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K.

(a)     Documents filed as part of this report:

        1.    The following financial statements of the Company are included in
              ITEM 8:
<TABLE>
<CAPTION>
                                                                                                PAGE
                                                                                                ----
<S>                                                                                             <C>
              Balance Sheet - December 31, 1998 and 1997                                           6
              Statement of Operations - Three Years Ended
                December 31, 1998                                                                  7
              Statement of Stockholder's Equity -
                Three Years Ended December 31, 1998                                                8
              Statement of Cash Flows -
                Three Years Ended December 31, 1998                                                9
              Notes to Financial Statements - December 31, 1998                                   10
</TABLE>

        2.    Financial Statement Schedules:  None.

              All schedules for which provision is made in the applicable
              accounting regulation of the Securities and Exchange Commission
              are not required under the related instructions or are
              inapplicable and, therefore, have been omitted.

        3.    Exhibits:

<TABLE>
<CAPTION>
              EXHIBIT
              NUMBER 
              -------
<S>                       <C>

                1.1       Underwriting Agreement dated as of September 26, 1997
                          by and among DLJSC, the Registrant and CMC(9)
                2.1       Stock Purchase Agreement dated as of August 10, 1994(4)
                3.1       Certificate of Amendment of the Certificate of
                          Incorporation of the Company dated August 9, 1994(4)
                3.2       Certificate of Incorporation(1)
                3.3       Bylaws(1)
                3.2       Certificate of Merger of the Company into CMCSC IV-A,
                          filed and Certified on December 21, 1995 with the
                          Secretary of State of Delaware(10)
                3.3       Bylaws of CMCSC IV-A(10)
                3.4       Certificate of Incorporation of CMCSC IV-A, as filed
                          with the Secretary of State of Delaware on December
                          13, 1995*
                4.1       Form of Indenture between Registrant and Texas
                          Commerce Bank, National Association, as Trustee(1)
                4.2       Form of First Supplement to the Indenture(5)
                4.3       Form of Second Supplement to the Indenture(6)
                4.5       Form of Fourth Supplement to the Indenture(9)
                4.4       Form of Third Supplement to the Indenture(7)
               10.1       Form of Pooling and Administrative Agreement(1)
               10.2       Form of Servicing Agreement(1)
               10.4       Management Agreement between Registrant and
                          Capstead Advisers, Inc. dated January 1, 1993(2)
               10.5       Amended Management Agreement between Registrant
                          and Capstead Advisers, Inc. dated October 1, 1993(3)
               23         Consent of Ernst & Young LLP, Independent Auditors*
</TABLE>


                                      -16-
<PAGE>   19
                                     PART IV

                              ITEM 14. - CONTINUED



        3.    Exhibits (continued):

<TABLE>
<CAPTION>
              EXHIBIT
              NUMBER 
              -------
<S>                       <C>

               27         Financial Data Schedule*
               28.1       Computational Materials provided by Donaldson, Lufkin
                          and Jenrette Securities Corporation(8)
</TABLE>

(b)     Reports on Form 8-K:

        Current Report on Form 8-K dated October 28, 1997 to file the following:

        Exhibit 28.1 - Computational Material provided by Donaldson, Lufkin and
        Jenrette Securities Corporation.

        Current Report on Form 8-K dated October 29, 1997 to file the following:

        Exhibit 1.1 - Underwriting Agreement dated as of October 28, 1997 by and
        among DLJSC, the Registrant and CMC.

        Exhibit 4.5 - Series 1997-2 Supplement relating to the Series 1997-2
        bonds.

        Current Report on Form 8-K/A dated November 17, 1997 to file the
        following:

        Exhibit 99.1 - Schedule of Zip code Listings related to the Fourth
        Supplement to the Indenture (Series 1997-NAMC 3).

(c)     Exhibits - The response to this section of ITEM 14 is submitted as a 
        separate section of this report.

-----------------

(1)      Incorporated herein by reference to the Company's Registration
         Statement on Form S-3 (No. 33-47912) filed May 14, 1992
(2)      Previously filed with the Commission as an exhibit to the Registrant's
         Annual Report on Form 10-K for the year ended December 31, 1992
(3)      Previously filed with the Commission as an exhibit to the Registrant's
         Annual Report on Form 10-K for the year ended December 31, 1993
(4)      Previously filed with the Commission as an Exhibit to the Registrant's
         Quarterly Report on Form 10-Q for the quarter ended June 30, 1994
(5)      Previously filed with the Commission as an exhibit to the Registrant's
         Current Report on Form 8-K on September 30, 1994
(6)      Previously filed with the Commission as an exhibit to the Registrant's
         Current Report on Form 8-K on October 31,1994
(7)      Previously filed with the Commission as an exhibit to the Registrant's
         Current Report on Form 8-K on December 30, 1994
(8)      Previously filed with the Commission as an exhibit to the Registrant's
         Current Report on Form 8-K on September 26, 1997
(9)      Previously filed with the Commission as an exhibit to the Registrant's
         Current Report on Form 8-K on September 30, 1997
(10)     Previously filed with the Commission as an exhibit to the Registrant's
         Current Report on Form 10-K for the year ended December 31, 1995
*        Filed herewith.


                                      -17-
<PAGE>   20

                                   SIGNATURES


Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the Company has duly caused this report to be signed on its behalf
by the undersigned, thereunto duly authorized.


                                             CMC SECURITIES CORPORATION IV
                                                      REGISTRANT


Date:  March 25, 1999                    By: /s/ ANDREW F. JACOBS            
                                             --------------------------------
                                                     Andrew F. Jacobs
                                             Executive Vice President-Finance,
                                                 Treasurer and Secretary


Pursuant to the requirements of the Securities Exchange Act of 1934, this report
has been signed below by the following persons on behalf of the Registrant and
in the capacities indicated below and on the dates indicated.


<TABLE>
<S>                                               <C>                                               <C>

/s/ RONN K. LYTLE                                  Chairman, Chief                                   March 29, 1999
------------------------------                      Executive Officer
     (Ronn K. Lytle)                                and Director



/s/ ANDREW F. JACOBS                               Executive Vice President -                        March 25, 1999
------------------------------                      Finance, Treasurer
    (Andrew F. Jacobs)                              and Secretary



/s/ MAURICE MCGRATH                                Director                                          March 26, 1999
-------------------------------
      (Maurice McGrath)
</TABLE>


                                      -18-
<PAGE>   21




SUPPLEMENTAL INFORMATION TO BE FURNISHED WITH REPORTS FILED PURSUANT TO SECTION
15(d) OF THE ACT BY REGISTRANTS WHICH HAVE NOT REGISTERED SECURITIES PURSUANT TO
SECTION 12 OF THE ACT.

No annual report or proxy material has been sent to security holders.


<PAGE>   22

                                 EXHIBIT INDEX

<TABLE>
<CAPTION>
              EXHIBIT
              NUMBER 
              -------
<S>                       <C>

                1.1       Underwriting Agreement dated as of September 26, 1997
                          by and among DLJSC, the Registrant and CMC(9)
                2.1       Stock Purchase Agreement dated as of August 10, 1994(4)
                3.1       Certificate of Amendment of the Certificate of
                          Incorporation of the Company dated August 9, 1994(4)
                3.2       Certificate of Incorporation(1)
                3.3       Bylaws(1)
                3.2       Certificate of Merger of the Company into CMCSC IV-A,
                          filed and Certified on December 21, 1995 with the
                          Secretary of State of Delaware(10)
                3.3       Bylaws of CMCSC IV-A(10)
                3.4       Certificate of Incorporation of CMCSC IV-A, as filed
                          with the Secretary of State of Delaware on December
                          13, 1995*
                4.1       Form of Indenture between Registrant and Texas
                          Commerce Bank, National Association, as Trustee(1)
                4.2       Form of First Supplement to the Indenture(5)
                4.3       Form of Second Supplement to the Indenture(6)
                4.5       Form of Fourth Supplement to the Indenture(9)
                4.4       Form of Third Supplement to the Indenture(7)
               10.1       Form of Pooling and Administrative Agreement(1)
               10.2       Form of Servicing Agreement(1)
               10.4       Management Agreement between Registrant and
                          Capstead Advisers, Inc. dated January 1, 1993(2)
               10.5       Amended Management Agreement between Registrant
                          and Capstead Advisers, Inc. dated October 1, 1993(3)
               23         Consent of Ernst & Young LLP, Independent Auditors*
               27         Financial Data Schedule*
               28.1       Computational Materials provided by Donaldson, Lufkin
                          and Jenrette Securities Corporation(8)
</TABLE>

-----------------

(1)      Incorporated herein by reference to the Company's Registration
         Statement on Form S-3 (No. 33-47912) filed May 14, 1992
(2)      Previously filed with the Commission as an exhibit to the Registrant's
         Annual Report on Form 10-K for the year ended December 31, 1992
(3)      Previously filed with the Commission as an exhibit to the Registrant's
         Annual Report on Form 10-K for the year ended December 31, 1993
(4)      Previously filed with the Commission as an Exhibit to the Registrant's
         Quarterly Report on Form 10-Q for the quarter ended June 30, 1994
(5)      Previously filed with the Commission as an exhibit to the Registrant's
         Current Report on Form 8-K on September 30, 1994
(6)      Previously filed with the Commission as an exhibit to the Registrant's
         Current Report on Form 8-K on October 31,1994
(7)      Previously filed with the Commission as an exhibit to the Registrant's
         Current Report on Form 8-K on December 30, 1994
(8)      Previously filed with the Commission as an exhibit to the Registrant's
         Current Report on Form 8-K on September 26, 1997
(9)      Previously filed with the Commission as an exhibit to the Registrant's
         Current Report on Form 8-K on September 30, 1997
(10)     Previously filed with the Commission as an exhibit to the Registrant's
         Current Report on Form 10-K for the year ended December 31, 1995
*        Filed herewith.