Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers

The registrant, Cubist Pharmaceuticals, Inc. ("Cubist"), held its Annual Meeting of Stockholders on June 4, 2009 (the "Annual Meeting"). At the Annual Meeting, the stockholders of Cubist approved an amendment to Cubist's Amended and Restated 1997 Employee Stock Purchase Plan, or ESPP, to increase the number of shares issuable under the ESPP by 500,000 shares. A brief description of the terms and conditions of the ESPP is set forth in Cubist's definitive proxy statement on Schedule 14A filed with the Securities and Exchange Commission on April 24, 2009 (the "Proxy Statement") under the heading "Proposal No. 2 - Approval of Amendment to Amended and Restated 1997 Employee Stock Purchase Plan to Increase the Number of Shares Issuable under the Plan by 500,000", and such description is incorporated herein by reference. A copy of the plan is attached as Appendix A to the Proxy Statement.

Item 8.01 Other Events

At the Annual Meeting, the stockholders of Cubist also approved an amendment to Cubist's Amended and Restated 2002 Directors' Equity Incentive Plan, or Directors' Plan, to extend the term of the Directors' Plan by three years and to increase the number of shares issuable under the Directors' Plan by 400,000 shares. A brief description of the terms and conditions of the Directors' Plan is set forth in the Proxy Statement under the heading "Proposal No. 3 - Approval of Amendment to Amended and Restated 2002 Directors' Equity Incentive Plan to Extend the Term of the Plan and Increase the Number of Shares Issuable under the Plan", and such description is incorporated herein by reference. A copy of the plan is attached as Appendix B to the Proxy Statement.

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