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


                                    FORM 8-K


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


                Date of Report (date of earliest event reported):
                                 April 22, 2004


                       Cabot Microelectronics Corporation
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             (Exact name of registrant as specified in its charter)


         Delaware                       000-30205                   36-4324765
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(State or other jurisdiction       (Commission File Number)     (IRS Employer
  of incorporation)                                             Identification)


                    870 Commons Drive, Aurora, Illinois 60504
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               (Address of principal executive offices) (Zip Code)

                                 (630) 375-6631
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              (Registrant's telephone number, including area code)

                                 Not applicable
           -----------------------------------------------------------
          (Former name or former address, if changed since last report)







Item 7.  Financial Statements and Exhibits.

         (c) Exhibits

             The following exhibits are filed herewith:

             99.1  Press release, dated April 22, 2004, entitled "Cabot
                   Microelectronics Reports Results For Second Fiscal Quarter
                   2004."

Item 12. Results of Operations and Financial Condition.

         On April 22, 2004, Cabot Microelectronics Corporation issued a press
release entitled "Cabot Microelectronics Reports Results For Second Fiscal
Quarter 2004," a copy of which is attached hereto as Exhibit 99.1 and
incorporated herein by reference. The press release contains financial and other
information including that related to our second fiscal quarter ended March 31,
2004. The press release also includes cautionary statements identifying
important factors that could cause actual results to differ materially from
those described by any forward-looking statements. This information shall not be
deemed "filed" for purposes of Section 18 of the Securities and Exchange Act of
1934, as amended (the "Exchange Act"), or incorporated by reference in any
filing under the Securities Act of 1933, as amended, or the Exchange Act, except
as shall be expressly set forth by specific reference in such a filing.



                                    SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned hereunto duly authorized.


                                            CABOT MICROELECTRONICS CORPORATION


Date: April 22, 2004                        By: /s/ WILLIAM S. JOHNSON
                                                --------------------------------
                                                William S. Johnson
                                                Vice President and Chief
                                                Financial Officer [Principal
                                                Financial Officer]


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                                INDEX TO EXHIBITS

Exhibit
Number        Title
--------      -----

 99.1         Press release, dated April 22, 2004, entitled "Cabot
              Microelectronics Reports Results For Second Fiscal Quarter 2004."




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