X0303 4 2010-10-06 0001070336 ACHILLION PHARMACEUTICALS INC ACHN 0001013425 TREU JESSE I C/O DOMAIN ASSOCIATES, LLC ONE PALMER SQUARE PRINCETON NJ 08542 0 0 1 0 Common Stock 2010-10-06 4 J 0 25000 A 25000 I By Domain Associates, LLC Transfer of shares to Domain Associates, LLC, from one of its Managing Members. The Reporting Person is a Managing Member of Domain Associates, LLC. Pursuant to Instruction (4)(b)(iv) of Form 4, the Reporting Person has elected to report as indirectly beneficially owned the entire number of securities beneficially owned by such entity. The Reporting Person disclaims beneficial ownership of any securities, and any proceeds thereof, that exceed his or her pecuniary interest therein and/or that are not actually distributed to him or her. The Reporting Person also indirectly beneficially owns (i) 7,972,968 shares held by Domain Partners VIII, L.P. and (ii) 59,161 shares held by DP VIII Associates, L.P. The Reporting Person is a Managing Member of One Palmer Square Associates VIII, LLC, which is the sole general partner of Domain Partners VIII, L.P. and DP VIII Associates, L.P. Pursuant to Instruction (4)(b)(iv) of Form 4, the Reporting Person has elected to report as indirectly beneficially owned the entire number of securities beneficially owned by each such entity. The Reporting Person disclaims beneficial ownership of any securities, and any proceeds thereof, that exceed his or her pecuniary interest therein and/or that are not actually distributed to him or her. /s/Kathleen K. Schoemaker, Attorney-in-Fact 2010-10-08