SEC Form 3 
FORM 3	UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940 	  
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1. Name and Address of Reporting Person*
ORBIMED ADVISORS LLC	

(Last)	(First)	(Middle)	
601 LEXINGTON AVE., 54TH FLOOR	

(Street) 
NEW YORK	NY	10022	

(City)	(State)	(Zip)	
	2. Date of Event Requiring Statement (Month/Day/Year)
10/04/2017 	3. Issuer Name and Ticker or Trading Symbol 
RHYTHM PHARMACEUTICALS, INC. [ RYTM ] 		
		4. Relationship of Reporting Person(s) to Issuer 
(Check all applicable) 
	Director	X	10% Owner	
	Officer (give title below)		Other (specify below)	
	
	5. If Amendment, Date of Original Filed (Month/Day/Year)				
			6. Individual or Joint/Group Filing (Check Applicable Line) 
	Form filed by One Reporting Person	
X	Form filed by More than One Reporting Person	
	
Table I - Non-Derivative Securities Beneficially Owned	
1. Title of Security (Instr. 4) 	2. Amount of Securities Beneficially Owned (Instr. 4) 	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 	4. Nature of Indirect Beneficial Ownership (Instr. 5) 	
Table II - Derivative Securities Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities) 	
1. Title of Derivative Security (Instr. 4) 	2. Date Exercisable and Expiration Date (Month/Day/Year)	3. Title and Amount of Securities Underlying Derivative Security (Instr. 4) 	4. Conversion or Exercise Price of Derivative Security 	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 	6. Nature of Indirect Beneficial Ownership (Instr. 5) 	
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares				
Series A Convertible Preferred Stock	(1) 	(1) 	Common Stock	2,546,295	0	I	See Footnote(2)(3) 	
1. Name and Address of Reporting Person*
ORBIMED ADVISORS LLC	

(Last)	(First)	(Middle)	
601 LEXINGTON AVE., 54TH FLOOR	

(Street) 
NEW YORK	NY	10022	

(City)	(State)	(Zip)	
	
1. Name and Address of Reporting Person*
OrbiMed Capital GP V LLC	

(Last)	(First)	(Middle)	
601 LEXINGTON AVE., 54TH FLOOR	

(Street) 
NEW YORK	NY	10022	

(City)	(State)	(Zip)	
	
1. Name and Address of Reporting Person*
ISALY SAMUEL D	

(Last)	(First)	(Middle)	
601 LEXINGTON AVE., 54TH FLOOR	

(Street) 
NEW YORK	NY	10022	

(City)	(State)	(Zip)	
	
Explanation of Responses:	
1. Upon the closing of the Issuer's initial public offering (the "IPO"), each share of the Issuer's series A convertible preferred stock (the "Series A Preferred") will automatically convert into shares of the Issuer's common stock on a 9.17-for-one basis for no consideration. The Series A Preferred has no expiration date.	
2. The shares of Series A Preferred reported 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 Advisers Act of 1940, as amended, is the sole managing member of GP V. Samuel D. Isaly ("Isaly") a natural person, is the managing member of, and holder of a controlling interest in, Advisors. By virtue of such relationships, GP V, Advisors and Isaly may be deemed to have voting and investment power with respect to the shares of Series A Preferred held by OPI V and as a result, may be deemed to have beneficial ownership over such shares of Series A Preferred.	
3. This report on Form 3 is jointly filed by GP V, Advisors and Isaly. Each of OPI V, GP V, Advisors and Isaly disclaims beneficial ownership of the securities reported herein for purposes of Rule 16a-1(a) under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), except to the extent of its or his pecuniary interest therein, if any. This report shall not be deemed an admission that any such entity or person is a beneficial owner of such securities for the purpose of Section 16 of the Exchange Act, or for any other purpose.	
	/s/ Samuel D. Isaly	10/04/2017	
	** Signature of Reporting Person	Date	
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.	
* If the form is filed by more than one reporting person, see Instruction 5 (b)(v).	
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).	
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.	
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