<PAGE>   1
                       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 [FEE REQUIRED]

For the fiscal year ended December 31, 1997

                                       OR

[ ]    TRANSITION REPORT PURSUANT TO SECTION 13 OF 15 (d) OF THE SECURITIES 
       EXCHANGE ACT OF 1934 [NO FEE REQUIRED]

For the transition period from ___________ to ____________

                         Commission file number 0-22572

                                 OM GROUP, INC.
               (Exact name of Registrant as specified in charter)

Delaware                                                     52-1736882
(State or other jurisdiction of                              (I.R.S. Employer
Incorporation or organization)                               Identification No.)

50 Public Square, 3800 Terminal Tower,  Cleveland, Ohio      44113-2204
(Address of principal executive offices)                     (Zip Code)

                                  216-781-0083
               Registrant's telephone number, including area code

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

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<S>                                                        <C>
        Title of each class                                Name of each exchange on which registered
        -------------------                                -----------------------------------------
Common Stock, par value $0.01 per share                                 New York Stock Exchange
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          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 the 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. [X]

     The aggregate market value of Common Stock, par value $.01 per share, held
by non-affiliates (based upon the closing sale price on the NYSE) on March 11,
1998 was approximately $983,655,959.

     As of March 11, 1998, there were 22,073,626 shares of Common Stock, par
value $.01 per share, outstanding.


                       DOCUMENTS INCORPORATED BY REFERENCE

Portions of the proxy statement for the annual meeting of stockholders to be
held on May 5, 1998 are incorporated by reference.


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                                    Page 12

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Part IV
Item 14                  *10.18     Employment Agreement between OM Group, Inc. and             **
                                    James M. Materna dated January 1, 1993.
                         *10.19     Employment Agreement between Mooney Chemicals,              **
                                    Inc. and Eugene Bak dated August 19, 1991.
                         *10.20     Amendment to Employment Agreement between Mooney            **
                                    Chemicals, Inc. and Eugene Bak dated September 1, 1992.
                         *10.21     Retirement Benefit Agreement, Eugene Bak,
                                    dated January 1, 1995 (filed as Exhibit to
                                    the Company's Annual Report on Form 10-K for
                                    the fiscal year ended December 31, 1995 and
                                    incorporated herein by reference).
                         *10.22     Employment Agreement between OM Group, Inc.                 **
                                    and Thomas E. Fleming dated August 19, 1991.
                         *10.23     Amendment to Employment Agreement between OM                **
                                    Group, Inc. and Thomas E. Fleming dated 
                                    August 19, 1991.
                         *10.24     Employment Agreement between Mooney Chemicals,              **
                                    Inc. and H. Burnham Tinker dated August 19, 1991.
                         *10.25     Amendment to Employment Agreement between OM                **
                                    Group, Inc. and H. Burnham Tinker dated 
                                    August 19, 1991.
                         *10.26     Employment Agreement between OM Group, Inc. 
                                    and Michael J. Scott (filed as Exhibit to the 
                                    Company's Annual Report on Form 10-K for the
                                    fiscal year ended December 31, 1994 and
                                    incorporated herein by reference).
                         *10.27     Employment Agreement between OM Group, Inc. 
                                    and J.R. Hwang (filed as Exhibit to the
                                    Company's Annual Report on Form 10-K for the
                                    fiscal year ended December 31, 1994 and
                                    incorporated herein by reference).
                         *10.28     Employment Agreement between OM Group, Inc. 
                                    and Terry L. Guckes (filed as Exhibit to the
                                    Company's Annual Report on Form 10-K for the
                                    fiscal year ended December 31, 1996 and
                                    incorporated herein by reference).
                         *10.29     Employment Agreement between OM Group, Inc.                 **
                                    and Antti Aaltonen.
                         *10.30     Employment Agreement between OM Group, Inc. 
                                    and John R. Holtzhauser and Amendment
                                    thereto (filed as Exhibit to the Company's
                                    Annual Report on Form 10-K for the fiscal
                                    year ended December 31, 1994 and
                                    incorporated herein by reference).
                          10.31     Stock Purchase Agreement between SUSI
                                    Corporation and OM Group, Inc. dated
                                    December 20, 1996 (filed as Exhibit to the
                                    Company's Annual Report on Form 10-K for the
                                    fiscal year ended December 31, 1996 and
                                    incorporated herein by reference).
                          10.32     Agreement and Plan of Merger between Auric 
                                    Corporation and OM Group, Inc. dated December 19, 
                                    1997.
                         +10.33     Joint Venture Agreement among OMG B.V.,
                                    Groupe George Forrest S.A., La Generale Des
                                    Carrieres Et Des Mines and OM Group, Inc. to
                                    partially or totally process the slag
                                    located in the site of Lumbumbashi,
                                    Democratic Republic of Congo.
                         +10.34     Agreement for Sale of concentrate production
                                    between Kokkola Chemicals Oy and La Generale
                                    Des Carriers Et Des Mines dated April 21,
                                    1997.
                         +10.35     Long Term Slag Sales Agreement between La
                                    Generale Des Carrieres Et Des Mines and J.V. Groupement
                                    Pour Le Traitment Du Terrill De Lubumbashi (filed
                                    as an annex to Exhibit 10.33 of the Company's Annual
                                    Report on Form 10-K for the fiscal year ended
                                    December 31, 1997).
                         +10.36     Long Term Cobalt Alloy Sales Agreement between J.V.
                                    Groupement Pour Le Traitement Du Terril De
                                    Lubumbashi and OMG Kokkola Chemicals Oy (filed
                                    as an annex to Exhibit 10.33 of the Company's Annual
                                    Report on Form 10-K for the fiscal year ended
                                    December 31, 1997).
                         +10.37     Tolling Agreement between Groupement Pour Le
                                    Traitement Du Terril De Lubumbashi and Societe
                                    De Traitement Du Terril De Lubumbashi (filed as
                                    an annex to Exhibit 10.33 of the Company's Annual
                                    Report on Form 10-K for the fiscal year ended
                                    December 31, 1997.
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                                    Page 13
Part IV
Item 14                    +     Portions of Exhibit have been omitted and
                                 filed separately with the Securities and 
                                 Exchange Commission in reliance on Rule
                                 246-2 and the Company's request for
                                 confidential treatment.

                           *     Indicates a management contract, executive 
                                 compensation plan or arrangement.

                           **    These documents were filed as exhibits to the
                                 Company's Form S-1 Registration Statement
                                 (Registration No. 33-60444) which became
                                 effective on October 12, 1993, and are
                                 incorporated herein by reference.

                           ***   Filed as Exhibit 99(b) to the OM Group, Inc.
                                 Form S-8 Registration Statement filed on
                                 February 1, 1994, and incorporated herein by
                                 reference.

                   (21) List of Subsidiaries (filed as a separate section of
                        this report)

                   (23) Consent of Ernst & Young LLP (filed as a separate
                        section of this report)

                   (24) Power of Attorney (filed as a separate section of this
                        report)

                   (27) Financial Data Schedule (filed as a separate section of
                        this report)

           (b) There were no reports filed on Form 8-K during the last quarter
                 of 1997.