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 AVENUE, 54TH FLOOR	

(Street) 
NEW YORK	NY	10022	

(City)	(State)	(Zip)	
	2. Date of Event Requiring Statement (Month/Day/Year)
10/16/2018 	3. Issuer Name and Ticker or Trading Symbol 
SI-BONE, Inc. [ SIBN ] 		
		4. Relationship of Reporting Person(s) to Issuer 
(Check all applicable) 
X	Director		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 6 Preferred Stock	(1) 	(1) 	Common Stock	572,326	(1)	I	By OrbiMed Private Investments V, L.P.(2)(3) 	
Series 7 Preferred Stock	(4) 	(4) 	Common Stock	179,404	(4)	I	By OrbiMed Private Investments V, LP(2)(3) 	
1. Name and Address of Reporting Person*
ORBIMED ADVISORS LLC	

(Last)	(First)	(Middle)	
601 LEXINGTON AVENUE, 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 AVENUE, 54TH FLOOR	

(Street) 
NEW YORK	NY	10022	

(City)	(State)	(Zip)	
	
Explanation of Responses:	
1. The Issuer's Series 6 Preferred Stock will automatically convert into approximately 1.05878 shares of Issuer's common stock immediately upon the closing of the Issuer's initial public offering and has no expiration date.	
2. Shares held by OrbiMed Private Investments V, LP. ("OPI V"). OrbiMed Capital GP V LLC ("GP V") is the general partner of OPI V and OrbiMed Advisors LLC ("OrbiMed Advisors") is the managing member of GP V. By virtue of such relationships, GP V and OrbiMed Advisors may be deemed to have voting and investment power with respect to the shares held by OPI V and as a result may be deemed to have have beneficial ownership of such shares. OrbiMed Advisors exercises investment and voting power through a management committee comprised of Carl L. Gordon, Sven H. Borho, and Jonathan T. Silverstein. David P. Bonita, a member of the Issuer's board of directors, is an employee of OrbiMed Advisors.	
3. This report on Form 3 is jointly filed by GP V and OrbiMed Advisors. 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 pecuniary interest therein, if any. This report shall not be deemed an admission that any such entity is a beneficial owner of such securities for purpose of Section 16 of the Exchange Act, or for any other purpose.	
4. The Issuer's Series 7 Preferred Stock will automatically convert into an equal number of shares of Issuer's common stock immediately upon the closing of the Issuer's initial public offering and has no expiration date.	
Remarks:	
	
	/s/ Douglas Coon, as attorney-in-fact	10/16/2018	
	** 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).	
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