Filed Pursuant to Rule 424(b)(3)
Registration No. 333-120055

PROSPECTUS SUPPLEMENT NO. 5 DATED SEPTEMBER 1, 2005
(TO PROSPECTUS DATED FEBRUARY 14, 2005)

VERTEX PHARMACEUTICALS INCORPORATED

$79,313,000 53/4% Convertible Senior Subordinated Notes Due 2011
5,308,800 Shares of Common Stock Issuable Upon Conversion of the Notes

        This Prospectus Supplement No. 4 supplements and amends the Prospectus dated February 14, 2005 (the "Prospectus"), relating to the resale from time to time by holders of our 53/4% Convertible Senior Subordinated Notes Due 2011 (the "Notes") and shares of our common stock issuable upon the conversion of the Notes. Such information has been obtained from the selling holders. This prospectus supplement should be read in conjunction with the Prospectus, which is to be delivered with this prospectus supplement.

        The information appearing in the table below, as of the date hereof, supplements and amends the information in the table appearing under the heading "Selling Holders" in the Prospectus, and, where the name of a selling holder identified in the table below also appears in the table in the Prospectus, the information set forth in the table below regarding that selling holder supercedes the information in the Prospectus:

Name of security holder
   Principal Amount of
Notes Beneficially
Owned and Offered(1)
   Number of shares
of Common Stock
Issuable Upon
Conversion of the Notes
that May Be Offered
Amaranth Helix Limited   2,500,000   167,336
Bank Austria Cayman Islands Ltd.   3,493,000   233,802
BP Amoco PLC Master Trust   644,000   43,106
Consolidated Pension Plan   325,000   21,754
Context Convertible Arbitrage Fund, LP   2,800,000   187,417
Context Convertible Arbitrage Offshore LTD   7,690,000   514,726
Clinton Multistrategy Master Fund, Ltd.   4,000,000   267,738
Delaware Street Capital Master Fund L.P.   1,000,000   66,935
Detroit Medical Center Endowment/Funded Dep. Fund (and) The Detroit Medical Center Guggenheim Portfolio Co. XV, LLC   483,000   32,329
Hotel Union & Hotel Industry of Hawaii Pension Plan   179,000   11,981
Institutional Benchmark Master Fund Ltd.   736,000   49,264
Institutional Benchmark Master Fund c/o Quattro Fund   1,307,000   87,484
National Bank of Canada   575,000   38,488
Quattro Fund Ltd.   15,552,000   1,040,964
Quattro Multistrategy Master Fund   541,000   36,212
Ramius, LP(2)   135,000   9,036
Ramius Capital Group(2)   645,000   43,173
Ramius Master Fund, Ltd.(2)   2,982,000   199,599
Ramius Partners II, LP(2)   129,000   8,635
         

RCG Multi Strategy Master Fund, Ltd.(2)   195,000   13,052
RCG Baldwin LP(2)   413,000   27,644
RCG Halifax Master Fund, Ltd.(2)   552,000   36,948
RCG Latitude Master Fund Ltd.(2)   5,262,000   352,209
Richmond Retirement System High Yield Fixed Income   150,000   10,040
Ritchie Capital Structure Arbitrage Trading, Ltd.   2,500,000   167,336
SSI Blended Market Neutral L.P.   356,000   23,829
SSI Hedged Convertible Market Neutral L.P.   402,000   26,908
Sphinx Convertible Arbitrage Fund SPC   625,000   41,834
Sphinx Convertible Arbitrage (Clinton) Segregated Portfolio   1,100,000   73,628
UBS Securities LLC(3)   8,793,000   588,554
Unidentified Securityholders   5,154,000   344,372
Univest Convertible Arbitrage Fund II Ltd (Norshield)(2)   275,000   18,407
Viacom Inc. Pension Plan Master Trust   58,000   3,882
Wachovia Securities International Ltd.   1,000,000   66,935
Xavex Convertible Arbitrage 5 Fund   161,000   10,776
(1)
The number of securities beneficially owned is determined under the rules of the Securities and Exchange Commission and the information is not necessarily indicative of beneficial ownership for any other purpose. Under those rules, beneficial ownership includes any securities as to which the individual has sole or shared voting power or investment power and also any securities which the individual has the right to acquire within 60 days after the date the selling holder provided this information, through the exercise of any stock option or other right. The inclusion in the table of securities, however, does not constitute an admission that the selling holders are direct or indirect beneficial owners of those securities. The selling holders have sole voting power and investment power with respect to all securities of capital stock listed as owned by the selling holders.

(2)
The selling securityholder is the affiliate of a registered broker-dealer, however the selling securityholder purchased the securities in the ordinary course of business and, at the time of purchase, had no agreements or understandings, directly or indirectly, with any person to distribute the securities.

(3)
UBS Securities LLC, a registered broker-dealer, acted as a dealer-manager in connection with the exchange of the old notes for the new notes. The securities to be sold by UBS Securities LLC hereunder were not issued or sold as underwriting compensation.

        The selling holders identified above may have sold, transferred or otherwise disposed of all or a portion of their Notes since the date on which they provided the information about their Notes in transactions exempt from the registration requirements of the Securities Act.