<PAGE>   1
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  FORM 10-K/A

                  Annual Report Pursuant to Section 13 or 15(d)
                     of the Securities Exchange Act of 1934

For the fiscal year ended June 30, 1998           Commission File Number 0-20348

                        D & K HEALTHCARE RESOURCES, INC.
             (Exact name of registrant as specified in its charter)

               Delaware                                  43-1465483
  (State or other jurisdiction of           (I.R.S. Employer Identification No.)
  incorporation or organization)

8000 Maryland Avenue, Suite 920, St. Louis, Missouri              63105
            (Address of principal executive offices)           (Zip Code)

Registrant's telephone number, including area code:  (314) 727-3485

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

Securities registered pursuant to Section 12(g) of the Act:  Common Stock, par 
value $.01
(Title of Class)

                  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. /x/

                  State the aggregate market value of the voting stock held by
non-affiliates of the registrant: approximately $40,903,904 as of September 17,
1998.

                  Indicate the number of shares outstanding of each of the
registrant's classes of common stock, as of the latest practicable date: As of
September 17, 1998, 3,756,775 shares of Common Stock, par value $.01, were
outstanding.

                       DOCUMENTS INCORPORATED BY REFERENCE

         Portions of the following documents are incorporated by reference in
the Part of this report indicated below:

Part II - Registrant's 1998 Annual Report to Stockholders

Part III -  B Registrant's Proxy Statement for its 1998 Annual Meeting of 
            Stockholders 
<PAGE>   2

                                    PART II


Item 8.           Financial Statements and Supplementary Data

                  The following financial statements and supplementary data,
included in the registrant's 1998 Annual Report to Stockholders, are
incorporated herein by this reference.
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                                                                                ANNUAL REPORT REFERENCE 
                                                                                -----------------------
<C>                                                                                    <C>
Report of Independent Public Accountants                                               Page 22
Consolidated Balance Sheets at June 30, 1998 and March 28, 1997                        Page 23
Consolidated Statements of Operations for the years ended
   June 30, 1998, March 28, 1997, and March 29, 1996 and for the                       Page 24
   three months ended June 30, 1997
Consolidated Statements of Stockholders' Equity for the years
   ended June 30, 1998, March 28, 1997, and March 29, 1996 and                         Page 25
   for the three months ended June 30, 1997
Consolidated Statements of Cash Flows for the years ended
   June 30, 1998, March 28, 1997, and March 29, 1996 and for the                       Page 26
   three months ended June 30, 1997
Notes to Consolidated Financial Statements                                             Page 27
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                                    PART III

Item 14.          Exhibits, Financial Statements, Schedules and Reports on Form 
                  8-K

                  (a)(1)   Financial statements:  Incorporated herein by        
reference, are listed in Item 8 of this report.


                     (2)   The following financial statement schedule and 
auditors' report thereon are included in Part IV of this report:

                                                                      Page

Report of Independent Public Accountants on Schedule                   12

Schedule II - Valuation and Qualifying Accounts                        13

     The Financial Statements of Pharmaceutical Buyers, Inc. for the years ended
     December 31, 1998 and 1997 included as Exhibit 99 to this Annual Report on
     Form 10-K/A are incorporated herein by this reference. 

                  Schedules other than those listed above have been omitted
because they are either not required or not applicable, or because the
information is presented in the consolidated financial statements or the notes
thereto.

                     (3)   Exhibits.

                           See Exhibit Index.

                  (b)      Reports on Form 8-K

                           None.

                  (c)      See Item 14(a)(3) above.*

                  (d)      See Item 14(a)(2) above.*


* Previously filed with Form 10-K for the year ended June 30, 1998.

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<PAGE>   4

                                   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.

                                                D & K HEALTHCARE RESOURCES, INC.
                                                          (Registrant)


                             By   /s/ J. Hord Armstrong, III
                                  --------------------------
                                  J. Hord Armstrong, III, Chairman of the Board
                                  and Chief Executive Officer 
Date:  March 30, 1999

                  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.

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Signature                                 Title                                           Date
---------                                 -----                                           ----
<C>                                       <C>                                             <C>
/s/ J. Hord Armstrong, III                Chairman of the Board and Chief                 March 30, 1999
------------------------------------      Executive officer
J. Hord Armstrong, III                    
                    
/s/ Martin D. Wilson                      President, Chief Operating Officer,
------------------------------------      Secretary and Director                          March 30, 1999
Martin D. Wilson                                                    

/s/ Thomas S. Hilton                      Senior Vice President,                          March 30, 1999
------------------------------------      Chief Financial Officer, 
Thomas S. Hilton                          (Principal Financial and Accounting Officer)

/s/ Richard F. Ford                       Director                                        March 30,1999
------------------------------------
Richard F. Ford

/s/ Bryan H. Lawrence                     Director                                        March 30, 1999
------------------------------------
Bryan H. Lawrence

/s/ Elliot H. Stein                       Director                                        March 30, 1999
------------------------------------
Elliot H. Stein

/s/ Robert E. Korenblat                   Director                                        March 30, 1999
------------------------------------
Robert E. Korenblat

/s/ Thomas F. Patton                      Director                                        March 30, 1999
------------------------------------
Thomas F. Patton

/s/ James M. Usdan                        Director                                        March 30, 1999
------------------------------------
James M. Usdan

/s/ Louis B. Susman                       Director                                        March 30, 1999
------------------------------------
Louis B. Susman
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                                  EXHIBIT INDEX
                                  -------------

Exhibit No.                               Description                                                          Page
-----------                               -----------                                                          ----
<S>                    <C>                                                                                     <C>
2.1                    Stock Purchase and Redemption Agreement, dated as of
                       November 30, 1995, by and among Pharmaceutical Buyers,
                       Inc., J. David McCay, The J. David McCay Living Trust,
                       Robert E. Korenblat and the registrant filed as Exhibit
                       2.4 to the registrant's Annual Report on Form 10-K for
                       the year ended March 28, 1997 is incorporated herein by
                       this reference.

3.1                    Restated Certificate of Incorporation, filed as Exhibit 3.2 to
                       registrant's Registration Statement on Form S-1 (Reg. No.
                       33-48730) is incorporated herein by this reference.

3.1a*                  Certificate of Amendment to the Restated Certificate of
                       Incorporation of D&K Wholesale Drug, Inc.

3.2                    By-laws of the registrant, as currently in effect, filed as
                       Exhibit 3.3 to registrant's Registration Statement on Form S-1
                       (Reg. No. 33-48730) is incorporated herein by this reference.

4.1                    Form of certificate for Common Stock, filed as Exhibit 4.1 to
                       registrant's Registration Statement on Form S-1 (Reg. No.
                       33-48730) is incorporated herein by this reference.

10.1                   Note Agreement, dated December 29, 1987, regarding
                       $3,250,000.00 11% Joint and Several Subordinated Notes
                       due December 29, 1997, and $1,750,000.00 11% Joint and
                       Several Convertible Subordinated Notes due December 29,
                       1997, by and among registrant, Delta Wholesale Drug,
                       Inc., W. Kelly Company, Wholesale Management Services,
                       Inc. and Massachusetts Mutual Life Insurance Company, and
                       amendments thereto, filed as Exhibit 10.3 to the
                       registrant's Registration Statement on Form S-1 (Reg. No.
                       33-48730) is incorporated herein by this reference.

10.2                   Note Agreement, dated December 29, 1987, regarding
                       $3,250,000.00 11% Joint and Several Subordinated Notes
                       due December 29, 1997, and $1,750,000.00 11% Joint and
                       Several Convertible subordinated Notes due December 29,
                       1997, by and among registrant, Delta Wholesale Drug,
                       Inc., W. Kelly Company, Wholesale Management Services,
                       Inc. and MassMutual Corporate Investors, and amendments
                       thereto, filed as Exhibit 10.4 to the registrant's
                       Registration Statement on Form S-1 (Reg. No. 
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Exhibit No.                               Description                                                          Page
-----------                               -----------                                                          ----
<S>                    <C>                                                                                     <C> 
                       33-48730) is incorporated herein by this reference.


10.3                   D & K Wholesale Drug, Inc.  Amended and Restated 1992 Long Term
                       Incentive Plan, filed as Annex A to the registrant's 1995 Proxy
                       Statement is incorporated herein by this reference.

10.4                   Wholesale Distribution Agreement, by and between registrant and
                       GLAXO INC., filed as Exhibit 10.14 to the registrant's
                       Registration Statement on Form S-1 (Reg. No. 33-48730) is
                       incorporated herein by this reference.

10.5                   Wholesale Distribution Agreement, dated January 1, 1995,
                       by and between registrant and SmithKline Beecham
                       Pharmaceuticals, filed as Exhibit 10.7 to registrant's
                       Annual Report on Form 10-K for the year ended March 29,
                       1996 is incorporated herein by this reference.

10.6                   Wholesale Prime Vendor Agreement, dated September 27,
                       1993, by and between registrant and Pfizer Inc., filed as
                       Exhibit 10.16 to the registrant's Annual Report on Form
                       10-K for the year ended April 1, 1994 is incorporated
                       herein by this reference.

10.7                   Warehousing and Distribution Service Agreement, dated July 1,
                       1994, by and between registrant and Eli Lilly and Company, filed
                       as Exhibit 10.17 to the registrant's Annual Report on Form 10-K
                       for the year ended April 1, 1994 is incorporated herein by this
                       reference.

10.8                   Amendment to Note Agreements, filed as Exhibit 10.21 to the
                       registrant's Registration Statement on Form S-1 (Reg. No.
                       33-48730) is incorporated herein by this reference.

10.9                   Letter Agreement dated May 24, 1994, between registrant,
                       Massachusetts Mutual Life Insurance Company and
                       MassMutual Corporate Investors, filed as Exhibit 10.30 to
                       the registrant's Annual Report on Form 10-K for the year
                       ended April 1, 1994 is incorporated herein by this
                       reference.

10.10                  Letter Agreement dated February 14, 1995, between
                       registrant, Massachusetts Mutual Life Insurance Company
                       and MassMutual Corporate Investors, filed as Exhibit
                       10.15 to the registrant's Annual Report on Form 10-K for
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Exhibit No.                               Description                                                          Page
-----------                               -----------                                                          ----                 
<S>                    <C>                                                                                     <C>
                       the year ended March 31, 1995 is incorporated herein by
                       this reference.

10.11                  Letter Agreement dated January 18, 1995, between
                       registrant, Massachusetts Mutual Life Insurance Company
                       and MassMutual Corporate Investors, filed as Exhibit
                       10.16 to the registrant's Annual Report on Form 10-K for
                       the year ended March 31, 1995 is incorporated herein by
                       this reference.

10.12                  Letter Agreement dated June 10, 1994, between registrant,
                       Massachusetts Mutual Life Insurance Company and
                       MassMutual Corporate Investors, filed as Exhibit 10.17 to
                       the registrant's Annual Report on Form 10-K for the year
                       ended March 31, 1995 is incorporated herein by this
                       reference.

10.13                  Letter Agreement dated October 10, 1994 between
                       registrant, Massachusetts Mutual Life Insurance Company
                       and MassMutual Corporate Investors, filed as Exhibit
                       10.18 to the registrant's Annual Report on Form 10-K for
                       the year ended March 31, 1995 is incorporated herein by
                       this reference.

10.14                  Supply Agreement dated April 18, 1995 by and between
                       registrant and M & H Drugs, Inc., filed as Exhibit 10.19
                       to the registrant's Annual Report on Form 10-K for the
                       year ended March 31, 1995 is incorporated herein by this
                       reference.

10.15                  Letter Agreement, dated August 31, 1993, by and between
                       registrant and W. VanMeter Alford, Jr. filed as Exhibit
                       10.28 to the registrant's Annual Report on Form 10-K for
                       the year ended April 1, 1994 is incorporated herein by
                       this reference.

10.16                  Third Amended and Restated Loan and Security Agreement,
                       dated as of March 3, 1995, by and among registrant,
                       Northern Drug Company, Krelitz Industries, Inc. and
                       Shawmut Capital Corporation, filed as Exhibit 10.21 to
                       the registrant's Annual Report on Form 10-K for the year
                       ended March 31, 1995 is incorporated herein by this
                       reference.

10.17                  First Amendment to Third Amended and Restated Loan and
                       Security Agreement, dated as of June 9, 1995, by and
                       among registrant, Northern Drug Company, Krelitz
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<PAGE>   8
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Exhibit No.                               Description                                                          Page
-----------                               -----------                                                          ----                 
<S>                    <C>                                                                                     <C>
                       Industries, Inc. and Shawmut Capital Corporation, filed
                       as Exhibit 10.22 to the registrant's Annual Report on
                       Form 10-K for the year ended March 31, 1995 is
                       incorporated herein by this reference.

10.18                  Second Amendment to Third Amended and Restated Loan and
                       Security Agreement and Consent, dated as of November 29,
                       1995 by and among Shawmut Capital Corporation, the
                       registrant, Northern Drug Company and Krelitz Industries,
                       Inc., filed as Exhibit 10.22 to the registrant's Annual
                       Report on Form 10-K for the year ended March 29, 1996 is
                       incorporated herein by this reference.

10.19                  Third Amendment to Third Amended and Restated Loan and
                       Security Agreement, Amendment to Pledge Agreement and
                       Waiver, dated as of July 1996, by and among Fleet Capital
                       Corporation, the registrant and Krelitz Industries, Inc.,
                       filed as Exhibit 10.23 to the registrant's Annual Report
                       on Form 10-K for the year ended March 29, 1996 is
                       incorporated herein by this reference.

10.20                  D & K Wholesale Drug, Inc. 401(k) Profit Sharing Plan and
                       Trust, dated January 1, 1995, filed as Exhibit 10.25 to
                       the registrant's Annual Report on Form 10-K for the year
                       ended March 29, 1996 is incorporated herein by this
                       reference.

10.21                  Amended and Restated Lease Agreement, dated as of January
                       16, 1996, by and between Morhaert Development, L.L.C. and
                       the registrant, filed as Exhibit 10.26 to the
                       registrant's Annual Report on Form 10-K for the year
                       ended March 29, 1996 is incorporated herein by this
                       reference.

10.22                  Fourth Amendment to Third Amended and Restated Loan and
                       Security Agreement, dated as of May 1997, by an among
                       Fleet Capital Corporation, the registrant and Krelitz
                       Industries, Inc. filed as Exhibit 10.28 to the
                       registrant's Annual Report on Form 10-K for the year
                       ended March 28, 1997 is incorporated herein by this
                       reference.

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EXHIBIT No.                               Description                                                          Page
-----------                               -----------                                                          ----                 
<S>                    <C>                                                                                     <C>
10.23                  Loan Agreement dated as of December 23, 1996, by and
                       among registrant, Krelitz Industries, Inc. and Magna
                       Bank, N.A., filed as Exhibit 10.30 to the registrant's
                       Annual Report on Form 10-K for the year ended March 28,
                       1997 is incorporated herein by this reference.

10.24*                 Pharmaceutical Services Agreement between Anthem Prescription
                       Management, Inc. and D&K Wholesale Drug, Inc. dated July 16, 1996.

10.25*                 Renewal dated June 26, 1998, to Pharmaceutical Services Agreement
                       between Anthem Prescription Management, Inc. and D&K Wholesale
                       Drug, Inc. dated July 16, 1996.

10.26*                 Purchase and Sale Agreement dated as of August 7, 1998 between D&K
                       Healthcare Resources, Inc., certain of its subsidiaries and D&K
                       Receivables Corporation.

10.27*                 Receivables Purchase Agreement dated as of August 7, 1998
                       among D&K Receivables Corporation, D&K Healthcare
                       Resources, Inc., Blue Keel Funding, LLC and Fleet
                       National Bank.

10.28*                 Fourth Amended and Restated Loan and Security Agreement dated as
                       of August 7, 1998 among D&K Healthcare Resources, Inc., Jaron
                       Inc., and Fleet Capital Corporation.

13*                    Registrant's 1998 Annual Report to Stockholders.

21*                    Subsidiaries of the registrant.

23*                    Consent of Arthur Andersen LLP.

99                     Pharmaceutical Buyers, Inc. Financial Statements as of December
                       31, 1998 and 1997 together with Report of  Independent Public
                       Accounts are filed herewith.
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* Previously Filed with Form 10-K for the year ended June 30, 1998.


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