Cubist Added to S&P SmallCap 600 Index

Lexington, MA, March 17, 2008 -- Cubist Pharmaceuticals, Inc. (NASDAQ: CBST) today announced that the company is now listed on the Standard & Poors (S&P) SmallCap 600 Index. The addition to the index is based on various criteria, including at least four consecutive quarters of positive as-reported earnings. 2007 was the first full year of GAAP profitability for Cubist, which has now reported six consecutive quarters of GAAP profitable performance.

About the S&P SmallCap 600
Introduced in 1994, the S&P SmallCap 600 covers approximately 3% of the U.S. Equities market. The index is designed to be an efficient portfolio of companies that meet specific inclusion criteria to ensure that they are investable and financially viable. More information on the S&P SmallCap 600 is available at www.indices.standardandpoors.com.

About Cubist
Cubist Pharmaceuticals, Inc. is a biopharmaceutical company focused on the research, development, and commercialization of pharmaceutical products that address unmet medical needs in the acute care environment. In the U.S., Cubist markets CUBICIN® (daptomycin for injection), the first antibiotic in a new class of anti-infectives called lipopeptides. The Cubist product pipeline includes pre-clinical programs that address unmet medical need in Gram-positive infections, Gram-negative infections, CDAD (Clostridium difficile-associated diarrhea), and HCV (Hepatitis C infections.) Cubist is headquartered in Lexington, MA. Additional information can be found at Cubist's web site at www.cubist.com.