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, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person *   ORBIMED ADVISORS LLC 2. Date of Event Requiring Statement (Month/Day/Year) 10/28/2014 3. Issuer Name and Ticker or Trading Symbol Sientra, Inc. [SIEN] (Last) (First) (Middle) 601 LEXINGTON AVENUE, 54TH FLOOR 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 Original Filed(Month/Day/Year) (Street) NEW YORK, NY 10022 6. Individual or Joint/Group Filing(Check Applicable Line) ___ Form filed by One Reporting Person _X_ Form filed by More than One Reporting Person (City) (State) (Zip) 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) Common Stock 3,155,260 I See Footnotes (1) (3) Common Stock 30,048 I See Footnotes (2) (3)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.			SEC 1473 (7-02)
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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 of Derivative Security: 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

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
ORBIMED ADVISORS LLC 601 LEXINGTON AVENUE, 54TH FLOOR NEW YORK, NY 10022	Â	  X	Â	Â
OrbiMed Capital GP III LLC 601 LEXINGTON AVENUE, 54TH FLOOR NEW YORK, NY 10022	Â	  X	Â	Â
ISALY SAMUEL D 601 LEXINGTON AVENUE, 54TH FLOOR NEW YORK, NY 10022	Â	  X	Â	Â

Signatures

/s/ Samuel D. Isaly		10/28/2014
**Signature of Reporting Person		Date

Explanation of Responses:

*	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).
(1)	These shares are held of record by OrbiMed Private Investments III, LP ("OPI III"). OrbiMed Capital GP III LLC ("GP III") is the general partner of OPI III, and OrbiMed Advisors LLC ("Advisors") is the managing member of GP III. Samuel D. Isaly ("Isaly"), a natural person, is the managing member of and owner of a controlling interest in Advisors. By virtue of such relationships, GP III, Advisors and Isaly may be deemed to have voting and investment power over the securities held by OPI III and as a result may be deemed to have beneficial ownership over such securities.
(2)	These shares are held of record by OrbiMed Associates III, LP ("Associates III"). Advisors is the general partner of Associates III. Isaly is the managing member of and owner of a controlling interest in Advisors. By virtue of such relationships, Advisors and Isaly may be deemed to have voting and investment power over the securities held by Associates III and as a result may be deemed to have beneficial ownership over such securities.
(3)	This report on Form 3 is jointly filed by GP III, Advisors, and Isaly. Each of the Reporting Persons 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. The Reporting Persons have designated a representative, currently Rishi Gupta, an employee of Advisors, to serve on the Issuer's board of directors. This report shall not be deemed an admission that any of the Reporting Persons is a beneficial owner for the purpose of Section 16 of the Exchange Act, or for any other purpose.

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