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

                                   FORM 10-Q

  X    QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE 
-----                                                                    
       SECURITIES EXCHANGE ACT OF 1934

FOR THE QUARTERLY PERIOD ENDED:  SEPTEMBER 30, 1997

                                      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:  33-5539

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

                 NEVADA                                    75-2449544
      (State or other jurisdiction of                   (I.R.S. Employer
       incorporation or organization)                  Identification No.)

     2711 NORTH HASKELL, DALLAS, TEXAS                       75204
  (Address of principal executive offices)                (Zip Code)

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

   (Former name, former address and former fiscal year, if changed from last
                                    report)

The Registrant meets the conditions set forth in General Instruction H(1)(a) and
(b) for Form 10-Q and is therefore filing this Form under the reduced disclosure
format.

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  _____

                     APPLICABLE ONLY TO CORPORATE ISSUERS:

Indicate the number of shares outstanding of each of the issuer's classes of
common stock, as of the last practicable date.

Common Stock ($1.00 par value)                    10,000 as of November 13, 1997

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<PAGE>
 
                         CMC SECURITIES CORPORATION I

                                   FORM 10-Q

                   FOR THE QUARTER ENDED SEPTEMBER 30, 1997


                                     INDEX

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

                       PART I. -- FINANCIAL INFORMATION

ITEM 1.   Financial Statements

 Balance Sheet -- September 30, 1997 (Unaudited)
  and December 31, 1996................................................ 1

 Statement of Operations -- Quarter and Nine Months Ended
  September 30, 1997 and 1996 (Unaudited).............................. 2

 Statement of Cash Flows -- Nine Months Ended
  September 30, 1997 and 1996 (Unaudited).............................. 3

 Notes to Financial Statements (Unaudited)............................. 4

ITEM 2.   Management's Discussion and Analysis of
          Financial Condition and Results of Operations................ 6

                         PART II. -- OTHER INFORMATION

ITEM 6.   Exhibits and Reports on Form 8-K............................. 6


SIGNATURES............................................................. 7
</TABLE> 
<PAGE>
 
                       PART I. -- FINANCIAL INFORMATION

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


ITEM 1.   FINANCIAL STATEMENTS

<TABLE>
<CAPTION>
                                       SEPTEMBER 30, 1997   DECEMBER 31, 1996
                                       ------------------   -----------------
<S>                                    <C>                  <C>    
                                           (UNAUDITED)         (UNAUDITED)
 
ASSETS
 Mortgage securities collateral              $585,602            $647,407      
 Cash and cash equivalents                          1                   1      
                                             --------            --------      
                                                                               
                                             $585,603            $647,408      
                                             ========            ========      
                                                                               
LIABILITIES                                                                    
 Collateralized mortgage securities          $585,602            $647,407      
 Accrued expenses                                  38                  30      
                                             --------            --------      
                                                                               
                                              585,640             647,437      
                                             --------            --------      
                                                                               
STOCKHOLDER'S EQUITY                                                           
 Common stock - $1 par value,                                                  
  10,000 shares authorized,                                                    
  issued and outstanding                           10                  10      
 Paid-in capital                                   83                  72      
 Accumulated deficit                             (130)               (111)     
                                             --------            --------      
                                                                               
                                                  (37)                (29)     
                                             --------            --------      
                                                          
                                             $585,603            $647,408
                                             ========            ========
</TABLE>

See accompanying notes to financial statements.
<PAGE>
 
                          CMC SECURITIES CORPORATION I

                            STATEMENT OF OPERATIONS
                                  (UNAUDITED)
                                 (IN THOUSANDS)

<TABLE>
<CAPTION>
                                        QUARTER ENDED     NINE MONTHS ENDED
                                         SEPTEMBER 30        SEPTEMBER 30
                                      -----------------  ------------------
                                       1997       1996    1997        1996
                                      -------   -------  --------   -------
<S>                                   <C>       <C>      <C>        <C>
Interest income on mortgage
 securities collateral                $11,241   $12,667   $34,691   $39,057
                                                
Interest expense on collateralized              
 mortgage securities                   10,879    12,261    33,579    37,808
                                      -------   -------   -------   -------
                                                
     Net interest income                  362       406     1,112     1,249
                                      -------   -------   -------   -------
                                                
Other expenses:                                 
 Management fees                            3         3         8         8
 Professional fees and other                2         1        11        10
 Pool insurance                           362       406     1,112     1,249
                                      -------   -------   -------   -------
                                                
   Total other expenses                   367       410     1,131     1,267
                                      -------   -------   -------   -------
                                                
Net loss                              $    (5)  $    (4)  $   (19)  $   (18)
                                      =======   =======   =======   =======
</TABLE>

See accompanying notes to financial statements.

                                      -2-
<PAGE>
 
                          CMC SECURITIES CORPORATION I

                            STATEMENT OF CASH FLOWS
                                  (UNAUDITED)
                                 (IN THOUSANDS)

<TABLE>
<CAPTION>
                                             NINE MONTHS ENDED SEPTEMBER 30
                                             -------------------------------
                                               1997                    1996
                                             --------                --------
<S>                                          <C>                    <C>
OPERATING ACTIVITIES:
 Net loss                                    $    (19)              $    (18)
 Noncash item - amortization of                                     
  discount and premium                            (28)                   (26)
 Net change in other assets and                                     
  accrued expenses                                  8                      8
                                             --------               --------
   Net cash used by                                                 
     operating activities                         (39)                   (36)
                                             --------               --------
                                                                    
INVESTING ACTIVITIES:                                               
 Mortgage securities collateral:                                    
  Principal collections on collateral          61,314                 57,690
  Decrease in accrued interest receivable         377                    357
  Decrease in short-term investments                3                      4
                                             --------               --------
   Net cash provided by                                             
     investing activities                      61,694                 58,051
                                             --------               --------
                                                                    
FINANCING ACTIVITIES:                                               
 Collateralized mortgage securities:                                
  Principal payments on securities            (61,314)               (57,690)
  Decrease in accrued interest payable           (352)                  (335)
 Capital contributions                             11                     10
                                             --------               --------
   Net cash used by financing                                       
     activities                               (61,655)               (58,015)
                                             --------               --------
                                                                    
Net change in cash and cash equivalents             -                      -
                                                                    
Cash and cash equivalents at beginning                              
 of period                                          1                      1
                                             --------               --------
                                                                    
Cash and cash equivalents at end of                                 
 period                                      $      1               $      1
                                             ========               ========
</TABLE>


See accompanying notes to financial statements.

                                      -3-
<PAGE>
 
                         CMC SECURITIES CORPORATION I

                         NOTES TO FINANCIAL STATEMENTS
                              SEPTEMBER 30, 1997
                                  (UNAUDITED)



NOTE A -- BASIS OF PRESENTATION

The accompanying unaudited financial statements have been prepared in accordance
with generally accepted accounting principles for interim financial information
and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X.
Accordingly, they do not include all of the information and footnotes required
by generally accepted accounting principles for complete financial statements.
In the opinion of management, all adjustments (consisting of normal recurring
accruals) considered necessary for a fair presentation have been included.
Operating results for the quarter and nine months ended September 30, 1997 are
not necessarily indicative of the results that may be expected for the calendar
year ending December 31, 1997.  For further information refer to the financial
statements and footnotes thereto included in the CMC Securities Corporation I
annual report on Form 10-K for the period ended December 31, 1996.

NOTE B -- DISCLOSURES REGARDING FAIR VALUES OF MORTGAGE SECURITIES COLLATERAL

The estimated fair values of mortgage securities collateral have been determined
by 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 could be realized 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 fair values of mortgage securities collateral were estimated using quoted
market prices, when available, including quotes made by Capstead Mortgage
Corporation's lenders in connection with designating collateral for repurchase
arrangements.

The following table summarizes the fair values of mortgage securities collateral
(in thousands):

<TABLE>
<CAPTION>
 
                               SEPTEMBER 30, 1997   DECEMBER 31, 1996
                               ------------------   -----------------
     <S>                       <C>                  <C>
     Carrying amount                $585,602            $647,407
     Unrealized gains                  9,913               5,620
     Unrealized losses                (1,783)             (7,865)
                                    --------            --------
 
      Fair value                    $593,732            $645,162
                                    ========            ========
</TABLE>

All mortgage securities collateral is held-to-maturity.  The maturity of
mortgage securities collateral is directly affected by the rate of principal
prepayments by mortgagors.  In addition, upon the redemption of remaining bonds
outstanding pursuant to clean-up calls, released collateral may be sold.  Such
sales are deemed maturities under the provisions of Statement of Financial
Accounting Standards No. 115.  No such redemptions occurred during the nine
months ended September 30, 1997 or during 1996.

                                      -4-
<PAGE>
 
NOTE C -- NET INTEREST INCOME ANALYSIS

The following table summarizes interest income and interest expense and the
average effective interest rates for the periods indicated (dollars in
thousands):

<TABLE>
<CAPTION>
                                              QUARTER ENDED SEPTEMBER 30
                                    ---------------------------------------------
                                           1997                        1996
                                    -----------------           -----------------
                                              AVERAGE                     AVERAGE
                                    AMOUNT     RATE             AMOUNT     RATE
                                    -------   -------           -------   -------
<S>                                 <C>       <C>               <C>       <C>
Interest income on mortgage
 securities collateral              $11,241    7.57%            $12,667    7.59%        
Interest expense on                                                                     
 collateralized mortgage                                                                
 securities                          10,879    7.33              12,261    7.35         
                                    -------                     -------          
Net interest income                 $   362                     $   406          
                                    =======                     =======          
</TABLE> 
 
<TABLE> 
<CAPTION> 
                                            NINE MONTHS ENDED SEPTEMBER 30
                                    ---------------------------------------------
                                           1997                        1996
                                    -----------------           -----------------
                                              AVERAGE                     AVERAGE
                                    AMOUNT     RATE             AMOUNT     RATE
                                    -------   -------           -------   -------
<S>                                 <C>       <C>               <C>       <C> 
Interest income on mortgage
 securities collateral              $34,691    7.53%            $39,057    7.59%        
Interest expense on                                                                    
 collateralized mortgage                                                               
 securities                          33,579    7.29              37,808    7.35         
                                    -------                     -------          
Net interest income                 $ 1,112                     $ 1,249          
                                    =======                     =======          
</TABLE>

The following table summarizes changes in interest income and interest expense
due to changes in interest rates, versus changes in volume for the quarter and
nine months ended September 30, 1997, compared to the same periods in 1996 (in
thousands):

<TABLE>
<CAPTION>
 
                                           QUARTER ENDED SEPTEMBER 30, 1997
                                        --------------------------------------
                                        RATE*          VOLUME*         TOTAL
                                        -----          -------         -------
<S>                                     <C>            <C>            <C>
Interest income on mortgage
 securities collateral                  $ (40)         $(1,386)       $(1,426)
Interest expense on                                                           
 collateralized mortgage                                                      
 securities                               (42)          (1,340)        (1,382)
                                        -----          -------        ------- 
                                        $   2          $   (46)       $   (44)
                                        =====          =======        ======= 
</TABLE> 

<TABLE> 
<CAPTION>  
                                         NINE MONTHS ENDED SEPTEMBER 30, 1997
                                        --------------------------------------
                                        RATE*          VOLUME*         TOTAL
                                        -----          -------        --------
<S>                                     <C>            <C>             <C> 
Interest income on mortgage
 securities collateral                  $(286)         $(4,080)       $(4,366)
Interest expense on                                                           
 collateralized mortgage                                                      
 securities                              (276)          (3,953)        (4,229)
                                        -----          -------        ------- 
                                        $ (10)         $  (127)       $  (137)
                                        =====          =======        ======= 
</TABLE>

*    THE CHANGE IN INTEREST DUE TO BOTH VOLUME AND RATE HAS BEEN ALLOCATED TO
     VOLUME AND RATE CHANGES IN PROPORTION TO THE RELATIONSHIP OF THE ABSOLUTE
     DOLLAR AMOUNTS OF THE CHANGE IN EACH.

                                      -5-
<PAGE>
 
ITEM 2.  MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
         OF OPERATIONS

FINANCIAL CONDITION AND RESULTS OF OPERATIONS
---------------------------------------------

CMC Securities Corporation I (the "Company"), was incorporated in Nevada on May
7, 1986 as a special-purpose finance corporation and is a wholly-owned
subsidiary of Capstead Mortgage Corporation ("CMC").

Since inception the Company has issued approximately $1.7 billion of
collateralized mortgage obligations ("CMOs").  The Company has not retained any
investment in the CMOs issued; therefore, no related economic benefit will be
received and no related net income or loss will be recognized other than the
amortization of unrecovered shelf issuance costs.  However, in instances where
an affiliate retained investments in these CMOs, the issuances were accounted
for as financings, and accordingly, the collateral and bonds are reflected on
the Company's balance sheet.  The Company has not issued any CMOs during 1997 or
1996.

The Company's net losses are due to operational costs incurred (management and
professional fees) and the amortization of unrecovered shelf issuance costs.

LIQUIDITY AND CAPITAL RESOURCES
-------------------------------

All ongoing CMO expenses of the Company 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 CMO expenses.  Cash flow requirements due to ongoing operational costs
are funded by CMC.

                          PART II. -- OTHER INFORMATION

ITEM 6.  EXHIBITS AND REPORTS ON FORM 8-K:

(a)  Exhibits:

     Exhibit 27 Financial Data Schedule (electronic filing only).

(b)  Reports on Form 8-K:  None.

                                      -6-
<PAGE>
 
                                   SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the
Registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.



                                        CMC SECURITIES CORPORATION I



Date:  November 13, 1997                By /s/ RONN K. LYTLE
                                           ------------------------------------
                                           Ronn K. Lytle
                                           Chairman and Chief Executive Officer


Date:  November 13, 1997                By /s/ ANDREW F. JACOBS
                                           ------------------------------------
                                           Andrew F. Jacobs
                                           Senior Vice President - Control
                                             and Treasurer

                                      -7-