August 12, 2024

Jeffrey Poulton
Chief Financial Officer
Alnylam Pharmaceuticals, Inc.
675 West Kendall Street
Henri A. Termeer Square
Cambridge, MA 20142

        Re: Alnylam Pharmaceuticals, Inc.
            Form 10-K for the Fiscal Year Ended December 31, 2023
            Filed February 15, 2024
            File No. 001-36407
Dear Jeffrey Poulton:

       We have limited our review of your filing to the financial statements 
and related
disclosures and have the following comments.

       Please respond to this letter within ten business days by providing the 
requested
information or advise us as soon as possible when you will respond. If you do 
not believe a
comment applies to your facts and circumstances, please tell us why in your 
response.

       After reviewing your response to this letter, we may have additional 
comments.

Form 10-K for the Fiscal Year Ended December 31, 2023
Notes to Consolidated Financial Statements
4. Net Revenues from Collaborations, page 107

1.     We note your tabular disclosure at the bottom of page 107 that 
quantifies the research and
       development (R&D) expenses incurred by collaborator and type that are 
directly
       attributable to your collaboration agreements. Please explain to us how 
this disclosure
       relates to your net revenues from collaborations. Using the Roche 
collaboration as an
       example, your disclosure on page 110 indicates that you recognized 
collaboration revenue
       of $24 million during 2023 related to your Development Services 
Obligation. Please
       explain how this amount relates to the $44.6 million in total R&D 
expenses attributed to
       the Roche collaboration as disclosed on page 107. In addition, to the 
extent applicable,
       please explain how the $547 million additional variable consideration 
attributed to cost
       reimbursement from development and manufacturing services and technology 
transfer
       related to the Roche Performance Obligations was calculated.
 August 12, 2024
Page 2

2.     Please explain the circumstances that resulted in a reversal of revenue 
in the amount of
       $15.5 million related to your Regeneron C5 License Obligation during 
2023 as disclosed
       on page 113.
       In closing, we remind you that the company and its management are 
responsible for the
accuracy and adequacy of their disclosures, notwithstanding any review, 
comments, action or
absence of action by the staff.

       Please contact Frank Wyman at 202-551-3660 or Angela Connell at 
202-551-3426 with
any questions.



                                                          Sincerely,

                                                          Division of 
Corporation Finance
                                                          Office of Life 
Sciences