<Page>

   AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON SEPTEMBER 1, 2004
                                               1933 ACT FILE NO. 333-______
                                               1940 ACT FILE NO. 811 - 03763


                  SECURITIES AND EXCHANGE COMMISSION
                        WASHINGTON, D.C. 20549

                       _______________________

                      REGISTRATION STATEMENT ON
                              FORM S-6

                      ________________________

          FOR REGISTRATION UNDER THE SECURITIES ACT OF 1933
               OF SECURITIES OF UNIT INVESTMENT TRUSTS
                     REGISTERED ON FORM N-8B-2

A. EXACT NAME OF TRUST:  CLAYMORE SECURITIES DEFINED PORTFOLIOS, SERIES 191

B. NAME OF DEPOSITOR:  CLAYMORE SECURITIES, INC.

C. COMPLETE ADDRESS OF DEPOSITOR'S PRINCIPAL EXECUTIVE OFFICES:

                      Claymore Securities, Inc.
                      2455 Corporate West Drive
                       Lisle, Illinois  60532

D. NAME AND COMPLETE ADDRESS OF AGENT FOR SERVICE:

Copies to:

   NICHOLAS DALMASO, ESQ.         ERIC F. FESS
   Senior Managing Director
   and General Counsel
   Claymore Securities, Inc.      Chapman and Cutler LLP
   2455 Corporate West Drive      111 West Monroe Street
   Lisle, Illinois  60532         Chicago, Illinois 60603
   (630) 505-3736                 (312) 845-3000

<Page>

     It is proposed that this filing will become effective (check appropriate
     box)

/ /  immediately upon filing pursuant to paragraph (b)

/ /  on (date) pursuant to paragraph (b)

/ /  60 days after filing pursuant to paragraph (a)

/ /  on (date) pursuant to paragraph (a) of rule 485 or 486

/ /  This post-effective amendment designates a new effective date for a
     previously filed post-effective amendment.

E. TITLE OF SECURITIES BEING REGISTERED:  Units of fractional undivided
beneficial interest.

F. APPROXIMATE DATE OF PROPOSED SALE TO PUBLIC: As soon as practicable after
the effective date of the Registration Statement.

/ /  Check box if it is proposed that this filing will become effective on
     (date) at (time) pursuant to Rule 487.

The registration hereby amends this Registration Statement on such date or
dates as may be necessary to delay its effective date until the registrant
shall file a further amendment which specifically states that this
Registration Statement shall thereafter become effective in accordance with
Section 8(a) of the Securities Act of 1933 or until the Registration
Statement shall become effective on such date as the Commission, acting
pursuant to said Section 8(a) may determine.

<Page>

            PRELIMINARY PROSPECTUS DATED SEPTEMBER 1, 2004

                       SUBJECT TO COMPLETION


[LOGO OMITTED]

Claymore Securities Defined Portfolios, Series 191

Peroni Growth Portfolio, Autumn 2004 Series


  Final prospectuses for prior Series of the Claymore Securities Defined
Portfolios are hereby incorporated by reference and used as part of a
preliminary prospectus for Claymore Securities Defined Portfolios, Series 191
(the "TRUST").  The final prospectus for the Trust is expected to be
substantially similar to the previous prospectuses.  However, specific
information with respect to the Trust, including pricing, the size and
composition of the Trust's portfolio, the number of units of the Trust, dates
and summary information regarding the characteristics of securities to be
deposited in the Trust is not now available and will be different from that
shown since Trust has a unique portfolio.  Accordingly, the information
contained herein with regard to the previous Trust should be considered as
being included for informational purposes only.

  The Securities and Exchange Commission has not approved or disapproved
these securities or passed upon the adequacy of this Prospectus.  Any
representation to the contrary is a criminal offense.

  The information in this Prospectus is not complete and may be changed. We
may not sell these securities until the registration statement filed with the
Securities and Exchange Commission is effective.  This Prospectus is not an
offer to sell the securities and it is not soliciting an offer to buy these
securities in any state where the offer or sale is not permitted.

Incorporated herein by reference is the prospectus from Claymore Securities
Defined Portfolios, Series 179 (Registration No. 333-115223) dated June 16,
2004 which shall be used as a preliminary prospectus for Claymore Securities
Defined Portfolios, Series 191.  The final prospectus for Claymore Securities
Defined Portfolios, Series 179, was filed pursuant to Rule 497 under the
Securities Act on June 17, 2004.

<Page>

                  CONTENTS OF REGISTRATION STATEMENT

  A. Bonding Arrangements of Depositor:

  The Depositor has obtained the following Securities Dealer Blanket Bond for
its officers, directors and employees:

       INSURER/POLICY NO.                        AMOUNT

  National Union Fire Insurance
Company of Pittsburgh, Pennsylvania              $250,000
           959-9000


  This Registration Statement comprises the following papers and documents.

        The Facing Sheet
        The Prospectus
        The Signatures
        Consents of Counsel

  The following exhibits:

1.1    Reference Trust Agreement (to be supplied by amendment).

1.1.1  Standard Terms and Conditions of Trust (Reference is made to
       Exhibit 1.1.1 to Amendment No.1 to the Registration Statement on
       Form S-6 for Claymore Securities Defined Portfolios, Series 116
       (File No. 333-72828 filed on December 18, 2001).

2.1    Code of Ethics (Reference is made to Exhibit 2.1 to the Registration
       Statement on Form S-6 for Claymore Securities Deferred Portfolios,
       Series 171 (File No. 333-112575 filed on February 19, 2004).

3.1    Opinion of counsel as to legality of the securities being registered
       including a consent to the use of its name in the Registration Statement
       (to be supplied by amendment).

3.2    Opinion of counsel as to Federal Income tax status of the securities
       being registered including a consent to the use of its name in the
       Registration Statement (to be supplied by amendment).

3.3    Opinion of counsel as to New York Income tax status of the securities
       being registered including a consent to the use of its name in the
       Registration Statement (to be supplied by amendment).

3.4    Opinion of counsel as to the Trustee and the Trust (s) including a
       consent to the use of its name in the Registration Statement (to be
       supplied by amendment).

4.1    Consent of Independent Registered Public Accounting Firm (to be
       supplied by amendment).

<Page>

                         SIGNATURES

  Pursuant to the requirements of the Securities Act of 1933, the Registrant,
Claymore Securities Defined Portfolios, Series 191 has duly caused this to
the Registration Statement to be signed on its behalf by the undersigned
thereunto duly authorized, in the City of Lisle, and State of Illinois, on
the 1st day of September, 2004.

                                       CLAYMORE SECURITIES DEFINED PORTFOLIOS,
                                         SERIES 191, Registrant

                                       By: CLAYMORE SECURITIES, INC., Depositor

                                               By: /s/ Nicholas Dalmaso
                                                   -----------------------
                                                        Nicholas Dalmaso

  Pursuant to the requirements of the Securities Act of 1933, this amended
Registration Statement has been signed below on September 1, 2004 by the
following persons, who constitute a majority of the Board of Directors of
Claymore Securities, Inc.

<Table>
<Caption>
SIGNATURE*                              TITLE**                         DATE
                                                               
                                                                     )  By: /s/ Nicholas Dalmaso
                                                                            ----------------------
                                                                     )            Nicholas Dalmaso
                                                                     )            Attorney in Fact*
                                                                     )
DAVID HOOTEN*                          Chairman of the Board of      )      September 1, 2004
                                       Directors                     )
                                                                     )
/S/ CHARLES MILLINGTON                 Chief Financial Officer              September 1, 2004
- ---------------------
    CHARLES MILLINGTON

/S/ NICHOLAS DALMASO                   Executive Vice President,            September 1, 2004
- --------------------                   Secretary, Treasurer and
    NICHOLAS DALMASO                   Director
</Table>

- ----------------------------

*   An executed copy of the related power of attorney was filed as Exhibit 6.0
    to Registration Statement No. 333-98345 on August 22, 2002.

**  The titles of the persons named herein represent their capacity in and
    relationship to Claymore Securities, Inc., the Depositor.

<Page>

             CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

  The consent of Grant Thornton LLP to the use of its report and to the
reference to such firm in the Prospectus included in the Registration
Statement will be filed as Exhibit 4.1 to the Registration Statement.

                      CONSENT OF CHAPMAN AND CUTLER LLP

  The consent of Chapman and Cutler LLP to the use of its name in the
Prospectus included in the Registration Statement will be contained in its
opinions to be filed as Exhibits 3.1 and 3.2 to the Registration Statement.

                   CONSENT OF EMMET, MARVIN & MARTIN LLP

  The consent of Emmet, Marvin & Martin LLP to the use of its name in the
Prospectus included in the Registration Statement will be contained in its
opinions to be filed as Exhibits 3.3 and 3.4 to the Registration Statement.

<Page>

                             MEMORANDUM
  Re:         Claymore Securities Defined Portfolios, Series 191

  The list of securities comprising the trust of the fund, the evaluation,
record and distribution dates and other changes pertaining specifically to
the new series, such as size and number of units of the trust in the fund and
the statement of financial condition of the new fund will be filed by
amendment.

                              1940 ACT

                       FORMS N-8A AND N-8B-2

  Form N 8A and Form N 8B 2 were filed in respect of Claymore Securities
Defined Portfolios, Series 116 (and subsequent series) (File No. 811-03763).

                              1933 ACT

                            THE INDENTURE

  The form of the proposed Standard Terms and Conditions of Trust is expected
to be in all respects consistent with the form of the Standard Terms and
Conditions of Trust dated December 18, 2001 relative to Claymore Securities
Defined Portfolios, Series 116.

                                                 CHAPMAN AND CUTLER LLP

Chicago, Illinois
September 1, 2004