<PAGE>   1

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

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


                               FORM 10-K/A NO. 1

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

        FOR THE FISCAL YEAR ENDED JUNE 30, 1998

[ ]     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 0-20740

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

                          PLATINUM SOFTWARE CORPORATION
             (Exact name of registrant as specified in its charter)


                    DELAWARE                                    33-0277592
        (State or other jurisdiction of                       (I.R.S Employer
         incorporation or organization)                      Identification No.)


                              195 TECHNOLOGY DRIVE
                          IRVINE, CALIFORNIA 92618-2402
               (Address of principal executive offices, zip code)

       REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE: (949) 453-4000

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

        SECURITIES REGISTERED PURSUANT TO SECTION 12(B) OF THE ACT: NONE
           SECURITIES REGISTERED PURSUANT TO SECTION 12(G) OF THE ACT:
                                 TITLE OF CLASS
                     COMMON STOCK, PAR VALUE $.001 PER SHARE

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

        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 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. [ ]

        The aggregate market value of the registrant's voting Common Stock held
by non-affiliates of the registrant was approximately $269,741,181 (computed
using the closing sales price of $13.25 per share of Common Stock on September
3, 1998 as reported by the Nasdaq National Market). Shares of Common Stock held
by each officer and director and each person who owns 5% or more of the
outstanding Common Stock have been excluded in that such persons may be deemed
affiliates. The determination of affiliate status is not necessarily a
conclusive determination for other purposes.

        There were 28,369,525 shares of the registrant's Common Stock, par value
$.001 per share, outstanding on September 3, 1998.

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

        Portions of the registrant's definitive Proxy Statement for the Annual
Meeting of Stockholders scheduled to be held on October 28, 1998, which Proxy
Statement will be filed no later than 120 days after the close of the
registrant's fiscal year ended June 30, 1998, are incorporated by reference in
Part III of this Annual Report on Form 10-K.


<PAGE>   2

                                     PART IV

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

         (a)(1) Financial Statements

                          Index to Financial Statements
                          -----------------------------
<TABLE>
<CAPTION>
                                                                                         Page
                                                                                         ----
<S>                                                                                      <C>
    Report of Independent Auditors......................................................  31

    Consolidated Balance Sheets as of June 30, 1997 and 1998............................  32

    Consolidated Statements of Operations for the years ended June 30, 1996, 
      1997 and 1998.....................................................................  33

    Consolidated Statements of Stockholders' Equity for the years ended June 30, 
      1996, 1997 and 1998...............................................................  34

    Consolidated Statements of Cash Flows for the years ended June 30, 1996, 
      1997 and 1998.....................................................................  35

    Notes to Consolidated Financial Statements..........................................  36

            (2) Financial Statement Schedules

                     Index to Financial Statement Schedules
                     --------------------------------------

    Report of Independent Auditors......................................................  48

    Schedule II - Valuation and Qualifying Accounts.....................................  49
</TABLE>

        All other schedules are omitted because they are not required or the
required information is included in the consolidated financial statements or
notes thereto.


                                       2

<PAGE>   3

             (3) Exhibits

                                INDEX TO EXHIBITS
<TABLE>
<CAPTION>

 Exhibit No.                                  Description                                  Location
 -----------                                  -----------                                  --------
<S>            <C>                                                                         <C>
    2.1        Agreement and Plan of Reorganization and Merger dated as of June 27, 1997      (9)
               among the Company, CSI Acquisition Corp., Clientele Software, Inc., Dale E.
               Yocum, Pamela Yocum, William L. Mulert (Schedules not included pursuant to
               Rule 601(b)(2) of Reg. S-K)
    2.2        Agreement and Plan of Reorganization dated as of November 4, 1997 by and      (11)
               among the Company, FS Acquisition Corp., FocusSoft, Inc., John Lococo,
               Michael Zimmerman and Joseph Brumleve (Schedules not included pursuant to
               Rule 601(b)(2) of Reg. S-K)
    3.1        Second Restated Certificate of Incorporation of the Company.                   (1)
    3.2        Certificate of Amendment to Second Restated Certificate of Incorporation      (10)
               of the Company
    3.3        Amended and Restated Bylaws of the Company, as currently in effect.            (8)
    3.6        Specimen Certificate of Common Stock.                                          (2)
    4.1        Certificate of Designation of Rights, Preferences and Privileges of            (4)
               Series A Junior Participating Preferred Stock
    4.2        Certificate of Designation of Preferences of Series B Preferred Stock          (5)
    4.3        Certificate of Designation of Preferences of Series C Preferred Stock          (6)
   10.1        Platinum Software Corporation Incentive Stock Option, Nonqualified Stock
               Option and Restricted Stock Purchase Plan - 1990 (the "1990 Plan").            (2)
   10.2        Form of Incentive Option Agreement pertaining to the 1990 Plan.                (2)
   10.3        Form of Nonqualified Stock Option Agreement pertaining to the 1990 Plan.       (2)
   10.4        Form of Restricted Share Agreement pertaining to the 1990 Plan.                (2)
   10.5        Form of Indemnification Agreement for Officers and Directors of the            (2)
               Company.
   10.6        Platinum Software Corporation Employee Stock Purchase Plan, as amended.        (2)
   10.10       1993 Nonqualified Stock Option Plan                                            (3)
   10.11       Form of Nonqualified Stock Option Agreement pertaining to the 1993             (3)
               Nonqualified Stock Option Plan.
   10.12       1994 Incentive Stock Option, Non-qualified Stock Option and Restricted         (5)
               Stock Purchase Plan.
   10.13       Form of Non-qualified Stock Option Agreement pertaining to the 1994 Plan.      (5)
   10.28       Stock Purchase Agreement dated September 22, 1994 between the Company and
               the Series B Preferred Stock Investors                                         (6)
   10.29       Registration Rights Agreement dated September 22, 1994 between the
               Company and the Series B Preferred Stock Investors                             (6)
   10.30       Amendment to Stock Purchase Agreement dated May 26, 1995 between the
               Company and the Series C Preferred Stock Investors                             (6)
   10.31       Amendment to Registration Rights Agreement dated May 26, 1995 between the
               Company and the Series C Preferred Stock Investors                             (6)
   10.33       Employment Offer letter with L. George Klaus dated February 7, 1996.           (7)
   10.34       Restricted Stock Purchase Agreement between the Company and L. George
               Klaus dated as of February 7, 1996.                                            (7)
   10.35       Employment Offer letter with William L. Pieser dated February 7, 1996.         (7)
   10.36       Restricted Stock Purchase Agreement between the Company and William L.
               Pieser dated as of February 7, 1996.                                           (7)
   10.42       Employment Offer letter with Ken Lally dated as of April 1, 1996.              (7)
   10.43       Restricted Stock Purchase Agreement between the Company and Ken Lally
               dated as of April 10, 1996.                                                    (7)
   10.44       1996 Nonqualified Stock Plan and Form of Nonqualified Option Agreement.       (12)
   10.45       Platinum Software Corporation Clientele Incentive Stock Plan.                 (12)
   10.47       1997 Nonqualified Stock Option Plan.                                          (13)
   10.48       Amended and Restated 1998 Nonqualified Stock Option Plan.
   10.49       Software Distribution License Agreement with FRx Software Corporation,  as
               amended to date. (Portions of this exhibit have been omitted pursuant to
               an application for confidential treatment.)                                   
   22.1        Subsidiaries of the Company.                                                  (14)
   23.1        Consent of Ernst & Young LLP.                                                 (14)
   24.1        Power of Attorney (included on the signature page of this Annual
               Report on Form 10-K).         
</TABLE>

                                       3


<PAGE>   4

                  Executive Compensation Plans and Arrangements

<TABLE>
<CAPTION>

 Exhibit No.                                  Description                                  Location
 -----------                                  -----------                                  --------
<S>            <C>                                                                         <C>
    10.1       1990 Plan                                                                     (2)
    10.2       Form of Incentive Option Agreement pertaining to the 1990 Plan.               (2)
    10.3       Form of Nonqualified Stock Option Agreement pertaining to the 1990 Plan.      (2)
    10.4       Form of Restricted Share Agreement pertaining to the 1990 Plan.               (2)
    10.10      1993 Nonqualified Stock Option Plan                                           (3)
    10.11      Form of Nonqualified Stock Option Agreement pertaining to the 1993
               Nonqualified Stock Option Plan.                                               (3)
    10.12      1994 Incentive Stock Option, Non-qualified Stock Option and Restricted
               Stock Purchase Plan.                                                          (5)
    10.13      Form of Non-qualified Stock Option Agreement pertaining to the 1994 Plan.     (5)
    10.33      Employment Offer letter with L. George Klaus dated February 7, 1996.          (7)
    10.34      Restricted Stock Purchase Agreement between the Company and L. George
               Klaus dated as of February 7, 1996.                                           (7)
    10.35      Employment Offer letter with William L. Pieser dated February 7, 1996.        (7)
    10.36      Restricted Stock Purchase Agreement between the Company and William L.
               Pieser dated as of February 7, 1996.                                          (7)
    10.42      Employment offer letter with Ken Lally dated as of April 1, 1996              (7)
    10.43      Restricted Stock Purchase Agreement between the Company and Ken Lally    
               dated as of April 10, 1996                                                    (7)
    10.44      1996 Nonqualified Stock Plan and Form of Nonqualified Option Agreement.      (12)
    10.45      Platinum Software Corporation Clientele Incentive Stock Plan.                (12)
    10.47      1997 Nonqualified Stock Option Plan.                                         (13)
    10.48      Amended and Restated 1998 Nonqualified Stock Option Plan.
</TABLE>

-------------------
 (1)  Incorporated by reference to the referenced exhibit number to the
      Company's Registration Statement on Form S-1, Reg. No. 33-57294.

 (2)  Incorporated by reference to the referenced exhibit number to the
      Company's Registration Statement on Form S-1, Reg. No. 33-51566.

 (3)  Incorporated by reference to the referenced exhibit to the Company's
      Annual Report on Form 10-K for the fiscal year ended June 30, 1993.

 (4)  Incorporated by reference to the referenced exhibit to the Company's
      Registration Statement on Form 8-A, dated April 14, 1994.

 (5)  Incorporated by reference to the referenced exhibit to the Company's
      Annual Report on Form 10-K for the fiscal year ended June 30, 1994.

 (6)  Incorporated by reference to the referenced exhibit to the Company's
      Annual Report on Form 10-K for the fiscal year ended June 30, 1995.

 (7)  Incorporated by reference to the referenced exhibit to the Company's
      Quarterly Report on Form 10-Q for the quarter ended March 31, 1996.

 (8)  Incorporated by reference to the referenced exhibit to the Company's
      Annual Report on Form 10-K for the fiscal year ended June 30, 1996.

 (9)  Incorporated by reference to the referenced exhibit to the Company's
      Current Report on Form 8-K dated June 30, 1997.


                                       4

<PAGE>   5

(10)  Incorporated by reference to the referenced exhibit to the Company's
      Quarterly Report on Form 10-Q for the quarter ending December 31, 1996.

(11)  Incorporated by reference to the referenced exhibit to the Company's
      Current Report on Form 8-K dated November 14, 1997.

(12)  Incorporated by reference to the referenced exhibit to the Company's
      Annual Report on Form 10-K for the fiscal year ended June 30, 1997.

(13)  Incorporated by reference to Exhibit 4.1 to the Company's Registration
      Statement on Form S-8, Reg. No. 333-41321.

(14)  Incorporated by reference to the referenced exhibit to the Company's
      Annual Report on Form 10-K for fiscal year ended June 30, 1998.

      (b) Reports on Form 8-K.

          The Company filed a current report on Form 8-K dated July 29, 1997 to
          report under Item 5, Other Events, the Company's results for the
          quarter and year ending June 30, 1997. In addition, the Company filed
          a current report on Form 8-K, dated October 29, 1997, to report under
          Item 5, Other Events, the Company's results for the quarter ending
          September 30, 1997. The Company also filed a Current Report on Form
          8-K dated November 25, 1997, to report under Item 2 "Acquisition or
          Disposition of Assets", the acquisition of FocusSoft, Inc. The Company
          also filed a Current Report on Form 8-K dated January 22, 1998, to
          report under Item 5 "Other Events" the Company's results for the
          quarter ending December 31, 1997.

The following trademarks may be mentioned in the foregoing Annual Report on 
Form 10-K: Platinum, Clientele, and SeQueL to Platinum. Platinum, Clientele and
SeQueL to Platinum are registered trademarks of the Company. All other product
names are trademarks or registered trademarks of their respective companies.


                                       5

<PAGE>   6

                                   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, in the City of Irvine,
State of California, on November 12, 1998.

                                      PLATINUM SOFTWARE CORPORATION


                                      By: /s/ L. GEORGE KLAUS
                                          ---------------------------------
                                          L. George Klaus
                                          President, Chief Executive Officer
                                          and Chairman of the Board

        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 and on the dates indicated.

<TABLE>
<CAPTION>

        SIGNATURE                    TITLE                            DATE         
        ---------                    -----                            ----         
<S>                          <C>                                 <C>               
/s/ L. GEORGE KLAUS          Chairman of the Board,              November 12, 1998 
------------------------     Chief Executive Officer                               
    L. George Klaus          And President                                         
                             (Principal Executive Officer)                         
                                                                                   
/s/ Paul G. Mazzarella       Vice President, Corporate           November 12, 1998 
------------------------     Controller (Principal Financial                       
    Paul G. Mazzarella       Accounting Officer)                                   
                                                                                   
                                                                                   
           *                 Director                            November 12, 1998 
------------------------                                                           
    W. Douglas Hajjar                                                              
                                                                                   
                                                                                   
           *                 Director                            November 12, 1998 
------------------------                                                           
    L. John Doerr                                                                  
                                                                                   
                                                                                   
           *                 Director                            November 12, 1998 
------------------------                                                           
    Arthur J. Marks                                                                
                                                                                   
                                                                                   
           *                 Director                            November 12, 1998 
------------------------
    Donald R. Dixon

*By: /s/ L. GEORGE KLAUS
------------------------
         L. George Klaus

</TABLE>

                                       6
<PAGE>   7
                                INDEX TO EXHIBITS
<TABLE>
<CAPTION>

 Exhibit No.                                  Description                                  Location
 -----------                                  -----------                                  --------
<S>            <C>                                                                         <C>
    2.1        Agreement and Plan of Reorganization and Merger dated as of June 27, 1997      (9)
               among the Company, CSI Acquisition Corp., Clientele Software, Inc., Dale E.
               Yocum, Pamela Yocum, William L. Mulert (Schedules not included pursuant to
               Rule 601(b)(2) of Reg. S-K)
    2.2        Agreement and Plan of Reorganization dated as of November 4, 1997 by and      (11)
               among the Company, FS Acquisition Corp., FocusSoft, Inc., John Lococo,
               Michael Zimmerman and Joseph Brumleve (Schedules not included pursuant to
               Rule 601(b)(2) of Reg. S-K)
    3.1        Second Restated Certificate of Incorporation of the Company.                   (1)
    3.2        Certificate of Amendment to Second Restated Certificate of Incorporation      (10)
               of the Company
    3.3        Amended and Restated Bylaws of the Company, as currently in effect.            (8)
    3.6        Specimen Certificate of Common Stock.                                          (2)
    4.1        Certificate of Designation of Rights, Preferences and Privileges of            (4)
               Series A Junior Participating Preferred Stock
    4.2        Certificate of Designation of Preferences of Series B Preferred Stock          (5)
    4.3        Certificate of Designation of Preferences of Series C Preferred Stock          (6)
   10.1        Platinum Software Corporation Incentive Stock Option, Nonqualified Stock
               Option and Restricted Stock Purchase Plan - 1990 (the "1990 Plan").            (2)
   10.2        Form of Incentive Option Agreement pertaining to the 1990 Plan.                (2)
   10.3        Form of Nonqualified Stock Option Agreement pertaining to the 1990 Plan.       (2)
   10.4        Form of Restricted Share Agreement pertaining to the 1990 Plan.                (2)
   10.5        Form of Indemnification Agreement for Officers and Directors of the            (2)
               Company.
   10.6        Platinum Software Corporation Employee Stock Purchase Plan, as amended.        (2)
   10.10       1993 Nonqualified Stock Option Plan                                            (3)
   10.11       Form of Nonqualified Stock Option Agreement pertaining to the 1993             (3)
               Nonqualified Stock Option Plan.
   10.12       1994 Incentive Stock Option, Non-qualified Stock Option and Restricted         (5)
               Stock Purchase Plan.
   10.13       Form of Non-qualified Stock Option Agreement pertaining to the 1994 Plan.      (5)
   10.28       Stock Purchase Agreement dated September 22, 1994 between the Company and
               the Series B Preferred Stock Investors                                         (6)
   10.29       Registration Rights Agreement dated September 22, 1994 between the
               Company and the Series B Preferred Stock Investors                             (6)
   10.30       Amendment to Stock Purchase Agreement dated May 26, 1995 between the
               Company and the Series C Preferred Stock Investors                             (6)
   10.31       Amendment to Registration Rights Agreement dated May 26, 1995 between the
               Company and the Series C Preferred Stock Investors                             (6)
   10.33       Employment Offer letter with L. George Klaus dated February 7, 1996.           (7)
   10.34       Restricted Stock Purchase Agreement between the Company and L. George
               Klaus dated as of February 7, 1996.                                            (7)
   10.35       Employment Offer letter with William L. Pieser dated February 7, 1996.         (7)
   10.36       Restricted Stock Purchase Agreement between the Company and William L.
               Pieser dated as of February 7, 1996.                                           (7)
   10.42       Employment Offer letter with Ken Lally dated as of April 1, 1996.              (7)
   10.43       Restricted Stock Purchase Agreement between the Company and Ken Lally
               dated as of April 10, 1996.                                                    (7)
   10.44       1996 Nonqualified Stock Plan and Form of Nonqualified Option Agreement.       (12)
   10.45       Platinum Software Corporation Clientele Incentive Stock Plan.                 (12)
   10.47       1997 Nonqualified Stock Option Plan.                                          (13)
   10.48       Amended and Restated 1998 Nonqualified Stock Option Plan.
   10.49       Software Distribution License Agreement with FRx Software Corporation,  as
               amended to date. (Portions of this exhibit have been omitted pursuant to
               an application for confidential treatment.)
   22.1        Subsidiaries of the Company.                                                  (14)
   23.1        Consent of Ernst & Young LLP.                                                 (14)
   24.1        Power of Attorney (included on the signature page of this Annual
               Report on Form 10-K).
</TABLE>
<PAGE>   8

<TABLE>
<CAPTION>

 Exhibit No.                                  Description                                  Location
 -----------                                  -----------                                  --------
<S>            <C>                                                                         <C>
    10.1       1990 Plan                                                                     (2)
    10.2       Form of Incentive Option Agreement pertaining to the 1990 Plan.               (2)
    10.3       Form of Nonqualified Stock Option Agreement pertaining to the 1990 Plan.      (2)
    10.4       Form of Restricted Share Agreement pertaining to the 1990 Plan.               (2)
    10.10      1993 Nonqualified Stock Option Plan                                           (3)
    10.11      Form of Nonqualified Stock Option Agreement pertaining to the 1993
               Nonqualified Stock Option Plan.                                               (3)
    10.12      1994 Incentive Stock Option, Non-qualified Stock Option and Restricted
               Stock Purchase Plan.                                                          (5)
    10.13      Form of Non-qualified Stock Option Agreement pertaining to the 1994 Plan.     (5)
    10.33      Employment Offer letter with L. George Klaus dated February 7, 1996.          (7)
    10.34      Restricted Stock Purchase Agreement between the Company and L. George
               Klaus dated as of February 7, 1996.                                           (7)
    10.35      Employment Offer letter with William L. Pieser dated February 7, 1996.        (7)
    10.36      Restricted Stock Purchase Agreement between the Company and William L.
               Pieser dated as of February 7, 1996.                                          (7)
    10.42      Employment offer letter with Ken Lally dated as of April 1, 1996              (7)
    10.43      Restricted Stock Purchase Agreement between the Company and Ken Lally    
               dated as of April 10, 1996                                                    (7)
    10.44      1996 Nonqualified Stock Plan and Form of Nonqualified Option Agreement.      (12)
    10.45      Platinum Software Corporation Clientele Incentive Stock Plan.                (12)
    10.47      1997 Nonqualified Stock Option Plan.                                         (13)
    10.48      Amended and Restated 1998 Nonqualified Stock Option Plan.
</TABLE>

-------------------
 (1)  Incorporated by reference to the referenced exhibit number to the
      Company's Registration Statement on Form S-1, Reg. No. 33-57294.

 (2)  Incorporated by reference to the referenced exhibit number to the
      Company's Registration Statement on Form S-1, Reg. No. 33-51566.

 (3)  Incorporated by reference to the referenced exhibit to the Company's
      Annual Report on Form 10-K for the fiscal year ended June 30, 1993.

 (4)  Incorporated by reference to the referenced exhibit to the Company's
      Registration Statement on Form 8-A, dated April 14, 1994.

 (5)  Incorporated by reference to the referenced exhibit to the Company's
      Annual Report on Form 10-K for the fiscal year ended June 30, 1994.

 (6)  Incorporated by reference to the referenced exhibit to the Company's
      Annual Report on Form 10-K for the fiscal year ended June 30, 1995.

 (7)  Incorporated by reference to the referenced exhibit to the Company's
      Quarterly Report on Form 10-Q for the quarter ended March 31, 1996.

 (8)  Incorporated by reference to the referenced exhibit to the Company's
      Annual Report on Form 10-K for the fiscal year ended June 30, 1996.

 (9)  Incorporated by reference to the referenced exhibit to the Company's
      Current Report on Form 8-K dated June 30, 1997.

(10)  Incorporated by reference to the referenced exhibit to the Company's
      Quarterly Report on Form 10-Q for the quarter ending December 31, 1996.

(11)  Incorporated by reference to the referenced exhibit to the Company's
      Current Report on Form 8-K dated November 14, 1997.

(12)  Incorporated by reference to the referenced exhibit to the Company's
      Annual Report on Form 10-K for the fiscal year ended June 30, 1997.

(13)  Incorporated by reference to Exhibit 4.1 to the Company's Registration
      Statement on Form S-8, Reg. No. 333-41321.

(14)  Incorporated by reference to the referenced exhibit to the Company's
      Annual Report on Form 10-K for fiscal year ended June 30, 1998.