United States securities and exchange commission logo

                          July 7, 2020

       John West
       President and Chief Executive Officer
       Personalis, Inc.
       1330 O   Brien Drive
       Menlo Park, CA 94025

                                                        Re: Personalis, Inc.
Statement on Form S-3
                                                            Filed July 2, 2020
                                                            File No. 333-239649

       Dear Mr. West:

              This is to advise you that we have not reviewed and will not
review your registration

               Please refer to Rules 460 and 461 regarding requests for
acceleration. We remind you
       that the company and its management are responsible for the accuracy and
adequacy of their
       disclosures, notwithstanding any review, comments, action or absence of
action by the staff.

                                                        Please contact Alan
Campbell at 202-551-4224 with any questions.


                          Division of Corporation Finance

                          Office of Life Sciences
       cc:                                              Peter Mandel