Mail Stop 3030
                                                                 August 28,
2018

     Via E-mail
     Laura A. Francis
     Chief Financial Officer
     SI-BONE, Inc.
     471 El Camino Real, Suite 101
     Santa Clara, California 95050

            Re:     SI-BONE, Inc.
                    Amendment No. 4 to Draft Registration Statement on Form S-1
                    Submitted July 31, 2018
                    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
     comments.

     Market Opportunity, page 4

     1.     It appears that the potential market for iFuse in the United States
has declined. Please
            disclose the reasons for the decline. Also, ensure your disclosure
on page 70 addresses
            any known trends or uncertainties related to this decline that are
reasonably expected to
            have a material effect on your results of operations.

     Contractual Obligations, page 80

     2.     Please revise to clarify the dollar amount of the contracts
excluded from the table based
            on the criteria mentioned in the last sentence of the second
paragraph of this section.
            Also tell us the authority on which you rely to exclude those
contracts from the table.
 Laura Francis
SI-BONE, Inc.
August 28, 2018
Page 2

        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, Senior
Attorney, at (202) 551-3641 with any other questions.

                                                          Sincerely,

                                                          /s/ Tom Jones for

                                                          Amanda Ravitz
                                                          Assistant Director
                                                          Office of Electronics
and Machinery


cc: Matthew B. Hemington