SecProbe.io

Mail Stop 3030
April 21, 2017

Via E -mail
Laura A. Francis
Chief Financial Officer
SI-BONE, Inc.
3055 Olin Avenue, Suite 2200
San Jose, California 95128

Re: SI-BONE, Inc.
Amendment No. 2 to Draft Registration Statement on Form S -1
Submitted March 27, 2017
 CIK No. 0001459839

Dear Ms. Francis:

We have reviewed your amended draft registration statement  and have the following
comments.  In some of our comments, we may ask you to provide us with information so we
may better understand your disclosure.

Please respond to this letter by providing the requested information and either submitting
an amended draft registration statement or publicly filing your registration stateme nt on
EDGAR.   If you do not believe our comments apply to your facts and circumstances or do not
believe an amendment is appropriate, please tell us why in your response.

After reviewing the information you provide in response to these  comments  and you r
amended draft registration statement or filed registration statement, we may have  additional
comments.

U.S. legislative or FDA or foreign regulatory reforms, page 43

1. Please update the disclosure in the third paragraph of this risk factor and the reference to
Exhibit 4.2 on page II -2.

Capitalization, page 60

2. We see on page 61 that 4,103,090 shares of common stock issuable upon the exercise of
the warrants outstandin g as of December 31, 2016 will be excluded from the pro forma
common shares outstanding calculation. Please reconcile the warrants underlying these
shares of common stock to the warrants disclosed on page F -23 in Note 9.

Laura Francis
SI-BONE, Inc.
April 21, 2017
Page 2

 Dilution, page 62

3. Please disclose how the numbers and percentages in the table on page 63 would change
assuming the exercise of all outstanding options and warrants.

Factors Affecting Results of Operations, page 65

4. It appears your market share in the United States has d eclined since 2015 while the total
market size for iFuse in the United States remains the same.  It also appears that your
revenues during prior fiscal years have increased only slightly.  Please expand the
disclosure in the third paragraph on page 66 and second paragraph on page 69 to clarify
the reasons for the market share decline and how it impacted your results of operations.
Ensure your disclosure addresses any known trends or uncertainties that are reasonably
expected to have a material effect on yo ur results of operations.  Please also revise to
clarify the effect that changes in price and/or volume had on the results you disclose.

Sales and Marketing Expenses, page 69

5. Your disclosure here refers to “lower headcount,” but your disclosure under “ Revenue”
indicates you expanded your direct sales force.  Please revise to clarify the impact of
headcount on your sales and marketing expenses.

Our Strategy, page 83

6. Please revise to discuss how the strategy you reference has maintained and enhanced
your leadership position, given the disclosure indicating your market share in the United
States has declined while the total market size for your iFuse product remains the same.

Manufacturing and Supply, page 106

7. Please expand to discuss the nature your agreement with rms Company, which is to be
filed as Exhibit 10.8.  Please also clarify the nature of each party’s obligations under this
agreement, as well as the agreement with Orchid.  For example, while we note t he
disclosures on pages 21 -22 regarding a lack of minimum manufacturing or purchasing
obligations, it is unclear how the prices you pay for components is determined and how
those prices effect your results of operations.

Principal Stockholders, page 136

8. Please revise to present the information in this section as of the most recent practicable
date, consistent with Item 403 of Regulation S -K.

Laura Francis
SI-BONE, Inc.
April 21, 2017
Page 3

 Note 10. Stock Option Plan, page F -24

9. You state in Item 15 on page II -3 that, “From June 2016 to March 2017, we issued and
sold an aggregate of 46,447,468 shares of our Series 7 preferred stock at $0.56 per
share.”  We see from your disclosure in this Note that the weighted average exercise price
of options issued is significantly less than the selling price of y our preferred stock during
the same period and less than the exercise price of options issued during 2015. In order to
assist us in evaluating your stock -based compensation, please provide us with the
following information for each date you granted stock o ptions in 2016 and the subsequent
periods:

• Date of grant;
• Number of shares issuable under the grants;
• Exercise price per share;
• Any restriction or vesting terms;
• Management´s estimate of the fair value of the underlying ordinary share;
• How management dete rmined the fair value estimate;
• How recent preferred share sales impacted the fair value estimate;
• Nature of any relationship between you and the recipient;
• Nature and terms of any concurrent transactions with the recipient; and
• The amount of any compensation for the grant.

When pricing information for this offering is available, please tell us the significant
reasons for any material differences between your last fair value determination and the
mid-point of the estimated IPO price range includin g all material positive and negative
events occurring during the period which could reasonably contribute to variances in fair
value.

Note 14. Net Loss Per Share of Common Stock, page F -30

10. Please revise the filing to provide a table supporting the calcu lation of pro forma
earnings per share and the pro forma weighted average -number of shares outstanding for
all periods presented.

Laura Francis
SI-BONE, Inc.
April 21, 2017
Page 4

 You may contact David Burton at (202) 551 -3626 or Kevin Kuhar, Accounting Branch
Chief, at (202) 551 -3662 if you have questio ns regarding comments on the financial statements
and related matters.  Please contact Tom Jones at (202) 551 -3602 or Geoff Kruczek, Special
Counsel, at (202) 551 -3641 with any other questions.

Sincerely,

 /s/ Geoff Kruczek for

 Amanda Ravitz
 Assistant Director
Office of Electronics and Machinery

cc: Matthew B. Hemington