<PAGE>  1
                                      UNITED STATES
                           SECURITIES AND EXCHANGE COMMISSION
                                 WASHINGTON, D.C.  20549

                                   FORM 10-K/A

                         AMENDMENT NUMBER 1 TO FORM 10-K
                      FOR THE YEAR ENDED DECEMBER 31, 1998


[X]              ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
                 EXCHANGE ACT OF 1934 For 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 1-13340

                      Mid Atlantic Medical Services, Inc.
             (Exact name of registrant as specified in its charter)

                              Delaware 52-1481661
                (State or other jurisdiction of (I.R.S. Employer
               incorporation or organization) Identification No.)

                    4 Taft Court, Rockville, Maryland 20850
              (Address of principal executive offices) (Zip Code)

                                 (301) 294-5140
   (Registrant's telephone number, including area code) Securities registered
                     pursuant to Section 12(b) of the Act:
                                            Name of Each Exchange
Title of Each Class                          on Which Registered
-------------------                         ---------------------
Common Stock, $0.01 par value               The New York Stock
  per share.                                  Exchange, Inc.

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

Indicate by check mark whether the registrant (1) has filed all 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
of Regulation S-K (Sec.  229.405 of this chapter) is not contained  herein,  and
will not be contained,  to the best of the 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.
[  ]

Aggregate  market  value  of  voting  and  non-voting   common  equity  held  by
non-affiliates computed by reference to the price at which the common equity was
sold,  or the average bid and asked price of such common  equity  March 4, 1999:
Approximately $405 million.

                      APPLICABLE ONLY TO CORPORATE REGISTRANTS:
Indicate the number of shares outstanding of each of the registrant's classes of
common stock, as of the latest practicable date.
                 51,134,162 shares of common stock as of March 4, 1999


<PAGE> 2
                       DOCUMENTS INCORPORATED BY REFERENCE
The Proxy  Statement for the  Registrant's  annual meeting of shareholders to be
held on April 26, 1999 is  incorporated  by reference into Part III of this Form
10-K, as supplemented by supplement dated April 2, 1999.


<PAGE> 3



                                     PART IV

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

(a)(1)
INDEX TO CONSOLIDATED FINANCIAL STATEMENTS                        PAGE
                                                                  ----
Consolidated Balance Sheets as of December 31, 1998 and 1997 ...    31
Consolidated Statements of Operations for the years ended
  December 31, 1998, 1997 and 1996 .............................    32
Consolidated Statements of Changes in Stockholders' Equity
  for the years ended December 31, 1998, 1997 and 1996 .........    33
Consolidated Statements of Cash Flows for the years ended
  December 31, 1998, 1997 and 1996 .............................    34
Notes to Consolidated Financial Statements .....................    35
Report of Ernst & Young LLP Independent Auditors ...............    54

(a)(2) and (d)
INDEX TO FINANCIAL STATEMENT SCHEDULE                             PAGE
                                                                  ----
II - Valuation and Qualifying Accounts as of December 31,
       1998, 1997 and 1996 .....................................    58

All other  schedules for which  provision is made in the  applicable  accounting
regulations of the Securities and Exchange  Commission are omitted  because they
are not required under the related instructions or are inapplicable.

The  page numbers listed above refer to the original Form 10-K filing.
<PAGE> 4
                         Mid Atlantic Medical Services, Inc.
                  Schedule II - Valuation and Qualifying Accounts
                              (in thousands)
<TABLE>
<CAPTION>
                                          Additions
                Balance at     ------------------------------
                Beginning        Charged to      Charged to                      Balance
                    of              Costs          Other        Deductions-       at End
Description       Period        and Expenses      Accounts      Write-Offs      of Period
-----------     ----------     -------------     ----------     -----------     ---------
<S>             <C>            <C>               <C>            <C>             <C>

DEDUCTED FROM ASSET ACCOUNTS:

YEAR ENDED DECEMBER 31, 1996
Allowance for doubtful accounts - accounts receivable

                $  3,638       $                 $  1,756(1)    $    (28)       $  5,366
                ========       ========          ========       ========        ========

Valuation allowance - deferred tax assets

                $    128       $                 $    634       $               $    762
                ========       ========          ========       ========        ========

YEAR ENDED DECEMBER 31, 1997
Allowance for doubtful accounts - accounts receivable

                $  5,366       $                 $    (93)(1)   $    (93)       $  5,180
                ========       ========          ========       ========        ========

Valuation allowance - deferred tax assets

                $    762       $                 $    325       $    (25)       $  1,062
                ========       ========          ========       ========        ========

YEAR ENDED DECEMBER 31, 1998
Allowance for doubtful accounts - accounts receivable

                $  5,180       $    143          $   (309)(1)   $    200        $ 5,214
                ========       ========          ========       ========        =======

Valuation allowance - deferred tax assets

                $  1,062       $  1,228          $              $               $ 2,290
                ========       ========          ========       ========        =======

</TABLE>

(1) The changes to the allowance were charged to premium revenue.







<PAGE> 5

(a)(3)
EXHIBITS

See the Exhibit Index on pages 7-9 of this Form 10-K/A.

(b)
REPORTS ON FORM 8-K

None.

<PAGE> 6
                               SIGNATURES

Pursuant to the  requirements  of Section 13 or 15(d) of the  Exchange  Act, and
Rule 12b-15 under the Exchange Act, the  registrant has caused this report to be
signed on its behalf by undersigned thereunto duly authorized.


      MID ATLANTIC MEDICAL SERVICES, INC. ("MAMSI")
      (Registrant)

      By: /s/  Robert E. Foss                   4/05/99
         --------------------------------------------------
        Robert E. Foss                                Date
         Senior Executive Vice President and Chief Financial Officer and
         Director
         (Principal Financial Officer)

<PAGE> 7
(a)(3), (b) and (c) List of Exhibits.


<TABLE>
<CAPTION>
                                  EXHIBIT INDEX
                                                                             Location of Exhibit
Exhibit                                                                        in Sequential
Number     Description of Document                                             Numbering System
-------    -----------------------                                           -------------------
<S>        <C>                                                               <C>
 3.1       Copy of Certificate of Incorporation of MAMSI dated
           October 7, 1986..........................................................(1)
 3.2       Copy of Certificate of Amendment of MAMSI Certificate of
           Incorporation dated April 23, 1990.......................................(4)
 3.3       Amended and Restated By-laws of MAMSI as of February 25, 1999............(14)
 3.4       Copy of Certificate of Amendment of MAMSI Certificate of
           Incorporation dated June 2, 1994.........................................(4)
10.5       Copy of Agreement between M.D. IPA and the United States
           Secretary of Health and Human Services dated December 20, 1985...........(1)
10.20      Copy of Amendments to Agreement between M.D. IPA and the United
           States Secretary of Health and Human Services dated December 24, 1987....(3)
10.26      1990 Non-Qualified Stock Option Plan.....................................(4)
10.27      Copy of 1990 Non-Qualified Stock Option Letter sent to Key Employees.....(4)
10.32      Copy of Contract between George T. Jochum and M.D. IPA for the period
           January 1, 1991 through January 1, 1994..................................(4)
10.35      1991 Non-Qualified Stock Option Plan.....................................(4)
10.36      Copy of 1991 Non-Qualified Stock Option Letter sent to Key Employees.....(4)
10.41      Copy of Agreement between M.D. IPA and Surgical Care Affiliates, Inc.,
           dated April 22, 1985.....................................................(4)
10.44      1992 Non-Qualified Stock Option Plan.....................................(4)
10.45      Copy of 1992 Non-Qualified Stock Option Letter sent to Key Employees.....(4)
10.48      Equipment Term Loan Agreement with Signet Bank dated March 25, 1991......(4)
10.50      Amendment to Revolving Loan Agreement with Signet Bank dated
           June 19, 1991............................................................(4)
10.53      Amendments to the Stock Option Plans effective May 15, 1991..............(4)
10.54      Summary Plan Description of the Employees Cash or Deferred Profit
           Sharing (401k) Plan dated October, 1991..................................(4)
10.55      Defined Benefit Plan Agreement with the Principal Financial Group which
           was approved September 12, 1991..........................................(4)
10.57      Mortgage and Loan Agreement with Aid Association for Lutherans dated
           October 4, 1990..........................................................(4)
10.60      1993 Non-Qualified Stock Option Plan.....................................(11)
10.61      1993 Non-Qualified Stock Option Letter Sent to Key Employees.............(11)
10.62      1992 Amendment to Employment Agreement Between George T. Jochum and
           the Company..............................................................(11)
10.65      Agreement to Purchase 2301 Research Boulevard dated September 30, 1993...(2)
10.66      1994 Management Bonus Program............................................(3)
10.67      1994 Non-Qualified Stock Option Plan.....................................(3)
10.68      1994 Non-Qualified Stock Option Letter sent to Key Employees.............(3)
10.69      Revolving Loan Agreement with Signet Bank dated September 30, 1993.......(3)
10.71      Agreement between OCI and the State of Maryland governing the Medical
           Assistance Program ("Medicaid") dated August 5, 1993.....................(3)
10.72      List of States in which MAMSI Life is Licensed to Operate................(3)
10.73      1995 Management Bonus Program............................................(4)
10.74      1995 Non-Qualified Stock Option Plan.....................................(4)
10.75      1995 Non-Qualified Stock Option Plan letter sent to Key Employees........(4)
10.76      Agreement between OCI and the Commonwealth of Virginia governing the
           Medical Assistance Program ("Medicaid") dated May 27, 1994...............(4)
10.77      1995 Amendment to Employment Agreement between George T. Jochum and
           the Company..............................................................(5)
10.78      1996 Management Bonus Program............................................(5)
10.79      1996 Non-Qualified Stock Option Plan.....................................(5)
10.80      Form of Agreement between MAMSI and Employees Granting Options
           under the 1996 Non-Qualified Stock Option Plan...........................(5)
10.81      Form of Agreement between MAMSI and George T. Jochum Granting Options
           under the 1996 Non-Qualified Stock Option Plan...........................(5)
10.82      Form of Agreement between MAMSI and Non-Employee Directors Granting
           Options under the 1996 Non-Qualified Stock Option Plan...................(5)
10         Amended and Restated Compensation Trust Agreement dated
           December 20, 1996........................................................(7)
10.1       Amended and Restated Common Stock Purchase Agreement dated
           December 20, 1996........................................................(7)
10.2       Replacement Promissory Note dated December 20, 1996......................(7)
10.83      1997 Management Bonus Program............................................(8)






<PAGE> 8
10.84      Form of Non-Qualified Stock Option Agreement for Options Granted
           under 1991, 1992, 1993, 1994 and 1995 Non-Qualified Stock Option Plan....(9)
10.85      Agreement of Purchase of Real Property by Mid-Atlantic
           Medical Services, Inc....................................................(10)
10.86      1997 Amendment to Employment Agreement between George T. Jochum
           and the Company..........................................................(11)
10.87      1998 Non-Qualified Stock Option Plan.....................................(11)
10.88      1998 Senior Management Bonus Plan........................................(11)
10.89      1998 Management Bonus Plan...............................................(11)
10.90      Amendment to 1994 Non-Qualified Stock Option Plan........................(11)
10.91      Amendment to 1995 Non-Qualified Stock Option Plan........................(11)
10.92      Amendment to 1996 Non-Qualified Stock Option Plan........................(11)
10.93      1999 Employment Agreement Between George T. Jochum and the Company.......(11)
10.94      Form of Agreement between MAMSI and Employees Granting Options
           under the 1998 Non-Qualified Stock Option Plan...........................(12)
10.95      Form of Agreement between MAMSI and George T. Jochum Granting Options
           under the 1998 Non-Qualified Stock Option Plan...........................(12)
10.96      Form of Agreement between MAMSI and Non-Employee Directors Granting
           Options under the 1998 Non-Qualified Stock Option Plan...................(12)
10.97      Memorandum to Employees and Form for Election Of Exchange
           and Repricing of Stock Options...........................................(12)
10.98      Agreement of Purchase and Sale of Real Estate............................(13)
10.981     1999 Non-Qualified Stock Option Plan-as Revised..........................
10.982     1999 Senior Management Bonus Plan........................................(14)
10.983     1999 Management Bonus Plan...............................................(14)
10.984     Amended and Restated Stock Compensation Trust Agreement
           dated January 11, 1999...................................................(14)
10.985     Common Stock Purchase Agreement dated January 11, 1999...................(14)
10.986     Allonge to Replacement Promissory Note dated January 11, 1999............(14)
10.987     Employment Agreement between the Company and Mark D. Groban..............(14)
10.988     Employment Agreement between the Company and Thomas P. Barbera...........(14)
10.989     Employment Agreement between the Company and Robert E. Foss..............(14)
10.990     Form of Executive Employment Agreement between the Company
           and Executive Staff......................................................(14)
10.991     Form of Agreement between MAMSI and Employees Granting Options
           under the 1999 Non-Qualified Stock Option Plan...........................(14)
10.992     Form of Agreement between MAMSI and Non-Employee Directors Granting
           Options under the 1999 Non-Qualified Stock Option Plan-as Revised........
21         Subsidiaries of the Company..............................................(14)
23         Consent of Independent Auditors..........................................(14)
27         Financial Data Schedule..................................................(14)
</TABLE>

(1) Incorporated by reference to exhibits filed with the Company's  Registration
Statement filed under the Securities Act of 1933 on Form S-4  (Registration  No.
33-9803).

(2)  Incorporated  by reference to exhibits  filed with the Company's  Quarterly
Report  filed  under the  Securities  Exchange  Act of 1934 on Form 10-Q for the
Quarterly Period Ended September 30, 1993.

(3) Incorporated by reference to exhibits filed with the Company's Annual Report
filed under the Securities Exchange Act of 1934 on Form 10-K for the fiscal year
ended December 31, 1993.

(4) Incorporated by reference to exhibits filed with the Company's Annual Report
filed under the Securities Exchange Act of 1934 on Form 10-K for the fiscal year
ended December 31, 1994.

(5)  Incorporated  by reference to exhibits  filed with the Company's  Quarterly
Report filed under the  Securities  Exchange Act on Form 10-Q for the  Quarterly
Period Ended March 31, 1995.

(6) Incorporated by reference to exhibits filed with the Company's Annual Report
filed under the Securities Exchange Act of 1934 on Form 10-K for the fiscal year
ended December 31, 1995.

(7)  Incorporated  by reference to exhibits  filed with the Company's  Quarterly
Report filed under the Securities  Exchange Act on Form 10-Q/A for the Quarterly
Period Ended September 31, 1996.

(8) Incorporated by reference to exhibits filed with the Company's Annual Report
filed under the Securities Exchange Act of 1934 on Form 10-K for the fiscal year
ended December 31, 1996.




<PAGE> 9

(9)  Incorporated  by reference to exhibits  filed with the Company's  Quarterly
Report filed under the  Securities  Exchange Act on Form 10-Q for the  Quarterly
Period Ended March 31, 1997.

(10)  Incorporated  by reference to exhibits filed with the Company's  Quarterly
Report filed under the  Securities  Exchange Act on Form 10-Q for the  Quarterly
Period Ended June 30, 1997.

(11)  Incorporated  by reference  to exhibits  filed with the  Company's  Annual
Report  filed  under the  Securities  Exchange  Act of 1934 on Form 10-K for the
fiscal year ended December 31, 1997.

(12)  Incorporated  by reference to exhibits filed with the Company's  Quarterly
Report filed under the  Securities  Exchange Act on Form 10-Q for the  quarterly
Period March 31, 1998.

(13)  Incorporated  by reference to exhibits filed with the Company's  Quarterly
Report filed under the  Securities  Exchange Act on Form 10-Q for the  Quarterly
Period Ended September 30, 1998.

(14)  Previously filed.