April 23, 2019

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

       Re: Personalis, Inc.
           Draft Registration Statement on Form S-1
           Submitted March 27, 2019
           CIK No. 0001527753

Dear Mr. West:

       We have reviewed your 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.

Draft Registration Statement on Form S-1 submitted March 27, 2019

General

1.     Please supplementally provide us with copies of all written
communications, as defined in
       Rule 405 under the Securities Act, that you, or anyone authorized to do
so on your behalf,
       present to potential investors in reliance on Section 5(d) of the
Securities Act, whether or
       not they retain copies of the communications
Use of Proceeds, page 63

2.     Please state the approximate amount of proceeds you intend to use for
each purpose
       listed. See Item 504 of Regulation S-K.
 John West
FirstName LastNameJohn West
Personalis, Inc.
Comapany NamePersonalis, Inc.
April 23, 2019
April 2 2019 Page 2
Page 23,
FirstName LastName
Management's Discussion and Analysis of Financial Condition and Results of
Operations
Results of Operations, page 77

3.       We note your revenues increased 302% from 2017 to 2018. You state that
this increase in
         revenues was primarily due to an increase in the volume of samples you
tested in relation
         to the sequencing and data analysis services you provided to our
customers. Please
         discuss in greater detail the underlying reasons for the material
increase in revenues, such
         as the reasons for in the increase in the volume of samples tested.
Additionally, if
         applicable, disclose whether the reasons for the change is a known
trend that you
         reasonably expect will have a material favorable impact on your
revenues. See Item
         303(a)(3) of Regulation S-K.
Principal Stockholders, page 148

4.       Please disclose the the address for each 5% beneficial owner. See Item
403(a) of
         Regulation S-K.
Note 2   Summary of Significant Accounting Policies
Fair Value of Common Stock, page F-13

5.       We may have additional comments on your accounting for equity
issuances including the
         stock options and other share-based compensation. Once you have an
estimated offering
         price, please provide us an analysis explaining the reasons for the
differences between
         recent valuations of your common stock leading up to the IPO and the
estimated offering
         price.
Note 3 - Revenues
Contract Assets and Liabilities, page F-16

6.       We note that you received large amounts of deposits from customers in
each of the years
         presented and that the balances of your contract liabilities have
grown from $5.6 million
         as of January 1, 2017 to $42.9 million as of December 31, 2018. We
also note your
         disclosure on page 13, that $37.3 million of the balance at December
31, 2018 relates to
         one customer. Please address the following points:
           Tell us how you considered the guidance in ASC paragraphs
606-10-32-15 through 19
             in determining the transaction price in these contracts and
whether a significant
             financing component exists.
           Explain to us the substantive business purpose of the large advance
payments.
           Tell us how you considered disclosing the growing balances as a
potential trend that
             may impact your cash from operations in future periods in your
discussion of liquidity
             and capital resources.
 John West
Personalis, Inc.
April 23, 2019
Page 3
Undertakings, page II-4

7.     Please add the undertakings required by Item 512(a)(5)(ii) and Item
512(a)(6) of
       Regulation S-K. Item 512(a)(5)(ii) is required for any prospectus filed
in reliance on Rule
       430C and Item 512(a)(6) is required for any offering that involves an
initial distribution of
       securities pursuant to Rule 159A. For guidance, refer to Securities Act
Rules Compliance
       and Disclosure Interpretation, Question 229.01.
Exhibits

8.     Please file the Convertible Promissory Note agreements identified on
page 146 as
       exhibits. See Item 601(b)(10) of Regulation S-K.
       You may contact James Giugliano at 202-551-3319 or Craig Arakawa at
202-551-3650 if
you have questions regarding comments on the financial statements and related
matters. Please
contact Michael Killoy at 202-551-7576 or Brigitte Lippmann at 202-551-3713
with any other
questions.



                                                             Sincerely,

FirstName LastNameJohn West                                  Division of
Corporation Finance
                                                             Office of
Beverages, Apparel and
Comapany NamePersonalis, Inc.
                                                             Mining
April 23, 2019 Page 3
cc:       Peter Mandel
FirstName LastName