RHYTHM PHARMACEUTICALS, INC. — Director's Dealing 2018

May 24, 2018

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: RHYTHM PHARMACEUTICALS, INC. (RYTM)
CIK: 0001649904
Period of Report: 2018-05-22

Reporting Person: ORBIMED ADVISORS LLC (10% Owner, See Remarks)
Reporting Person: OrbiMed Capital GP V LLC (10% Owner, See Remarks)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2018-05-22	Common Stock	S	17980	$30.38	Disposed	2751679	Indirect
2018-05-22	Common Stock	S	1600	$30.96	Disposed	2750079	Indirect

Footnotes

F1: The price reported in Column 4 is a weighted average price. These shares of the Issuer's common stock ("Shares") were sold in multiple transactions at prices ranging from $29.90 to $30.89 inclusive. Upon request, the Reporting Persons undertakes to provide the Issuer, any security holder of the Issuer, or the Securities and Exchange Commission (the "SEC") full information regarding the Shares purchased at each separate price within the range set forth in this footnote.

F2: The price reported in Column 4 is a weighted average price. These Shares were sold in multiple transactions at prices ranging from $30.90 to $31.10 inclusive. Upon request, the Reporting Persons undertakes to provide the Issuer, any security holder of the Issuer, or the SEC full information regarding the Shares purchased at each separate price within the range set forth in this footnote.

F3: These securities are held of record by OrbiMed Private Investments V, LP ("OPI V"). OrbiMed Capital GP V LLC ("GP V") is the sole general partner of OPI V, and OrbiMed Advisors LLC ("Advisors"), a registered adviser under the Investment Advisors Act of 1940, as amended, is the sole managing member of GP V. By virtue of such relationships, GP V and Advisors may be deemed to have voting and investment power with respect to the securities held by OPI V noted above and as a result may be deemed to beneficially own such securities for purposes of Rule 13d-3 under the Securities Exchange Act of 1934, as amended (the "Exchange Act"). Advisors exercised this investment and voting power through a management committee comprised of Carl L. Gordon, Sven H. Borho and Jonathan T. Silverstein, each of whom disclaims beneficial ownership of the Shares held by OPI V.

F4: This report on Form 4 is jointly filed by GP V and Advisors. Each of the Reporting Persons disclaims beneficial ownership of the securities reported herein for purposes of Rule 16a-1(a) under the Exchange Act, except to the extent of its pecuniary interest therein, if any. This report shall not be deemed an admission that any of the Reporting Persons is a beneficial owner of such securities for the purpose of Section 16 of the Exchange Act, or for any other purpose.