X0306 4 2016-12-12 0 0001178670 ALNYLAM PHARMACEUTICALS, INC. ALNY 0001180432 MARAGANORE JOHN C/O ALNYLAM PHARMACEUTICALS, INC 300 THIRD STREET CAMBRIDGE MA 02142 1 1 0 0 Chief Executive Officer Common Stock 2016-12-12 4 M 0 30151 22.75 A 171080 D Common Stock 2016-12-12 4 F 0 22710 42.61 D 148370 D Common Stock 2841 I by Managed Account Stock Option (right to buy) 22.75 2016-12-12 4 M 0 30151 0 D 2016-12-14 Common Stock 30151 0 D Represents a "net exercise" of outstanding stock options due to expire on December 14, 2016, as permitted under the governing ALNY stock incentive plan. These shares were withheld by ALNY for payment of the option exercise price and applicable tax withholding, based on the closing price of ALNY common stock on December 12, 2016. The reporting person owns 2,841 shares of ALNY common stock under the ALNY 401(k) plan as a result of the ALNY 401(k) matching contribution program. The stock option vested as to 25% of the shares on the first anniversary of the date of the stock option grant and as to an additional 6.25% of the shares each successive three month period thereafter. /s/ Michael P. Mason, Attorney-in-Fact for John M. Maraganore 2016-12-14