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                                                         Chicago, IL 60603-4080

CHAPMAN AND CUTLER LLP                                   T 312.845.3000
----------------------------------------                 F 312.701.2361
Attorneys at Law - Focused on Finance(R)                 www.chapman.com




                               September 28, 2018



Securities and Exchange Commission
100 F Street, NE
Washington, D.C.  20549


     Re:           Advisors Disciplined Trust 1921 (the "Fund")
                                  (CIK# 1741153)
                   --------------------------------------------

Ladies and Gentlemen:

     Transmitted herewith on behalf of Advisors Asset Management, Inc. (the
"Sponsor"), depositor and principal underwriter of the Fund, is the Registration
Statement on Form S-6 for the registration under the Securities Act of 1933 (the
"Securities Act") of units representing the ownership of interests in the unit
investment trust of the Fund (the "Trust").

     The Trust is a unit investment trust which will invest in a portfolio of
securities that includes shares of open-end management investment companies
registered under the Investment Company Act of 1940. The Registration Statement
has been prepared in substantial conformity with materials submitted on behalf
of Advisors Disciplined Trust 1884, declared effective by the Securities and
Exchange Commission (the "Commission") on July 20, 2018 (File No. 333-223976).
Such registration statement is a prior series of the Fund with a substantially
similar registration statement. We are requesting review of the Registration
Statement because the Fund is unable to rely on Rule 487 under the Securities
Act so that the Registration Statement would automatically become effective upon
filing.  The Fund may not rely on Rule 487 because paragraph (b)(1) of Rule 487
requires that reliance upon the rule is conditioned upon the registrant not
engaging in the business of investing in open-end funds.  Were it not for this
provision in Rule 487, it would be our opinion that the Registration Statement
would not contain disclosures which would render it ineligible to become
effective pursuant to Rule 487.  Accordingly we request limited review of the
Registration Statement only to the extent necessary to comply with Rule
487(b)(1).

     We have been advised that the Sponsor would like to activate the Fund and
have the Registration Statement declared effective on January 23, 2019, or as
soon as possible thereafter. An appropriate amendment to the Registration
Statement to reflect such deposit will be promptly filed with the Commission at
that time, accompanied by the request of the Sponsor that the Registration
Statement be made effective.

     No notification of registration or registration statement under the
Investment Company Act of 1940 is currently being submitted to the Commission,
as the filings under Investment Company Act File No. 811-21056 for Advisors
Disciplined Trust are intended to be applicable to this series of the Fund.

     Inasmuch as the Fund is not yet operative, no filings have been required
under any of the acts administered by the Commission. Therefore, for purposes of
Securities Act Release No. 5196 there are no delinquencies to be reported or
other references to be made to filings under the Securities Exchange Act of
1934.

     If you have any questions, please do not hesitate to contact Scott R.
Anderson at (312) 845-3834 or Matthew T. Wirig at (312) 845-3432.




                                Very truly yours,

                                /s/ CHAPMAN AND CUTLER LLP
                                --------------------------
                                    CHAPMAN AND CUTLER LLP