<PAGE>

                                 UNITED STATES
                      SECURITIES AND EXCHANGE COMMISSION

                            Washington, D.C. 20549

                                   FORM 10-K/A

(Mark One)
[X]  ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE
     ACT OF 1934

     For the fiscal year ended December 31, 2002

                                               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 001-13672

                            The Commerce Group, Inc.
             (Exact name of registrant as specified in its charter)

             Massachusetts                              04-2599931
     (State or other jurisdiction           (IRS Employer Identification No.)
            of incorporation)

            211 Main Street                               01570
       Webster, Massachusetts                           (Zip Code)
(Address of principal executive offices)

       Registrant's telephone number, including area code: (508) 943-9000

           Securities registered pursuant to Section 12(b) of the Act:

                                                      Name of each Exchange
    Title of each Class                                on Which Registered
    -------------------                                -------------------
Common Stock, $.50 Par Value Per Share               New York Stock Exchange

           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 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. [ ]

         Indicate by check mark whether the registrant is an accelerated filer
(as defined in Exchange Act Rule 12b-2). Yes [X] No [ ]

         The aggregate market value of the common stock held by non-affiliates
of the registrant, computed by reference to the price at which the common stock
was last sold, as of June 30, 2003, was $786,766,166.

<PAGE>

ITEM 15. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K

A.       (1)      The financial statements and notes to financial statements are
                    filed as part of this report in "Part II Item 8".

         (2)      The financial statement schedules are listed in the Index to
                    Consolidated Financial Statement Schedules.

         (3)      The exhibits are listed in the Index to Exhibits.

B.       No reports on Form 8-K were filed during the quarter ended December 31,
         2002.

<PAGE>

                                       SIGNATURES

         Pursuant to the requirements of Section 13 or 15(d) 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.

Dated: November 25, 2003

                                          THE COMMERCE GROUP, INC.

                                          By: /s/ Arthur J. Remillard, Jr.
                                             -----------------------------------
                                             Arthur J. Remillard, Jr.
                                             President, Chief Executive Officer,
                                             and Chairman of the Board

<PAGE>

                    THE COMMERCE GROUP, INC. AND SUBSIDIARIES
                              INDEX TO EXHIBITS(A)

<TABLE>
<CAPTION>
EXHIBIT
NUMBER                                     TITLE
------                                     -----
<S>               <C>
3.1               Articles of Organization, as amended (B)

3.2               By-Laws (B)

4                 Stock Certificate (B)

10.8*             1994 Management Incentive Plan as amended (C)

10.18*            Form of Non-Qualified Stock Option Agreement (D)

10.19*            Form of Incentive Stock Option Agreement (D)

10.20*            Form of Non-Qualified Stock Option Agreement (D)

10.21*            Form of Stock Option Agreement (D)

10.23*            Form of Book Value Award Agreement (E)

10.24             Reinsurance Agreement with Employers Reinsurance
                  Corporation(F)

10.25*            2002 Amended & Restated Incentive Compensation Plan (G)

10.26             ACIC Agent Growth Option Agreement (G)

10.27             Form of AAA Marketing Agreement (H)

10.28             Form of AAA Service Agreement (H)

10.29             Massachusetts Insurance Processing Service Agreement between
                  CGI Information Systems & Management Consultants Inc. and the
                  Registrant, as amended

10.30             Letter Agreement regarding growth options between AAA Southern
                  New England and the Registrant

21.1              Subsidiaries of the Registrant (G)

31.1              Rule 13a-14(a)/15d-14(a) Certification

31.2              Rule 13a-14(a)/15d-14(a) Certification
</TABLE>

(A)  Exhibits other than those listed are omitted because they are not required
     or are not applicable. Copies of exhibits are available without charge by
     writing to the Assistant to the President at 211 Main Street, Webster, MA
     01570.

(B)  Incorporated herein by reference to the exhibit with the same exhibit
     number, filed as an exhibit to the Registrant's Registration Statement on
     Form S-18 (No. 33-12533-B).

(C)  Incorporated herein by reference to the exhibit with the same exhibit
     number, filed as an exhibit to the Registrant's Form 10-Q for the period
     ended September 30, 1997.

(D)  Incorporated herein by reference to the exhibit with the same exhibit
     number, filed as an exhibit to the Registrant's Form 10-K for the year
     ended December 31, 1999.

(E)  Incorporated herein by reference to the exhibit with the same exhibit
     number, filed as an exhibit to the Registrant's Form 10-Q for the period
     ended June 30, 2002.

(F)  Incorporated herein by reference to the exhibit with the same exhibit
     number, filed as an exhibit to the Registrant's Form 10-Q for the period
     ended September 30, 2002.

<PAGE>

(G)  Filed as an exhibit to the Registrant's Form 10-K for the year ended
     December 31, 2002.

(H)  Filed as an exhibit to the Registrant's Form 10-K/A for the year ended
     December 31, 2002, filed on September 29, 2003

* Denotes management contract or compensation plan or arrangement.