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