Mail Stop 3030
                                                                  April 21,

     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 statement 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 your
     amended draft registration statement or filed registration statement, we
may have additional

     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 outstanding 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
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 declined 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 your 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 the
       disclosures on pages 21-22 regarding a lack of minimum manufacturing or
       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
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 your
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 options in 2016
and the subsequent

                 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 determined the fair value estimate;
                 How recent preferred share sales impacted the fair value
                 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 including all material
positive and negative
       events occurring during the period which could reasonably contribute to
variances in fair

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

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


                                                          /s/ Geoff Kruczek for

                                                          Amanda Ravitz
                                                          Assistant Director
                                                          Office of Electronics
and Machinery

cc: Matthew B. Hemington