<PAGE>
 
   
AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON FEBRUARY 11, 1994.     
 
                                                       REGISTRATION NO. 33-51383
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                                ---------------
                                 
                              AMENDMENT NO. 2     
                                       TO
                                    FORM S-4
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933
 
                                ---------------
 
                            FIRST BANK SYSTEM, INC.
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)
 
                                ---------------
 
       DELAWARE                      6711                      41-0255900
   (STATE OR OTHER            (PRIMARY STANDARD             (I.R.S. EMPLOYER
   JURISDICTION OF                INDUSTRIAL             IDENTIFICATION NUMBER)
   INCORPORATION OR           CLASSIFICATION CODE
    ORGANIZATION)                   NUMBER)
 
                                FIRST BANK PLACE
                            601 SECOND AVENUE SOUTH
                       MINNEAPOLIS, MINNESOTA 55402-4302
                                 (612) 973-1111
  (ADDRESS, INCLUDING ZIP CODE, AND TELEPHONE NUMBER, INCLUDING AREA CODE, OF
                   REGISTRANT'S PRINCIPAL EXECUTIVE OFFICES)
 
                                ---------------
 
                                RICHARD A. ZONA
                                FIRST BANK PLACE
                            601 SECOND AVENUE SOUTH
                       MINNEAPOLIS, MINNESOTA 55402-4302
                                 (612) 973-1111
 (NAME, ADDRESS, INCLUDING ZIP CODE, AND TELEPHONE NUMBER, INCLUDING AREA CODE,
                             OF AGENT FOR SERVICE)
 
                                   COPIES TO:
          LEE R. MITAU, ESQ.                     R. HENRY KLEEMAN, ESQ.
           DORSEY & WHITNEY                 WILDMAN, HARROLD, ALLEN & DIXON
        220 SOUTH SIXTH STREET                   225 WEST WACKER DRIVE
  MINNEAPOLIS, MINNESOTA 55402-1498           CHICAGO, ILLINOIS 60606-1229
 
                                ---------------
 
  APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: As soon as
practicable after the effective date of this Registration Statement.
 
  If any of the securities being registered on this Form are being offered in
connection with the formation of a holding company and there is compliance with
General Instruction G, check the following box. [_]
 
                                ---------------
 
  THE REGISTRANT 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>
 

                                    PART II
 
                     INFORMATION NOT REQUIRED IN PROSPECTUS
 
ITEM 21. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES.
 
  (a) EXHIBITS.
 

<TABLE>
     <C>  <S>                                                              <C>
     23.3 Consent of Ernst & Young (relating to financial statements of
           First Bank System, Inc. and Colorado National Bankshares,
           Inc.)
     23.4 Consent of Price Waterhouse (relating to financial statements
           of Boulevard Bancorp, Inc.)
     23.5 Consent of Deloitte & Touche (relating to financial statements
           of Western Capital Investment Corporation)
</TABLE>

 
 
                                      II-1

<PAGE>
 

                                   SIGNATURES
   
  PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THE REGISTRANT
HAS DULY CAUSED THIS AMENDMENT NO. 2 TO THE REGISTRATION STATEMENT TO BE SIGNED
ON ITS BEHALF BY THE UNDERSIGNED, THEREUNTO DULY AUTHORIZED, IN THE CITY OF
MINNEAPOLIS, STATE OF MINNESOTA, ON FEBRUARY 11, 1994.     
 
                                          First Bank System, Inc.
 
                                                  /s/ John F. Grundhofer
                                          By __________________________________
                                                    John F. Grundhofer
                                               Chairman, President and Chief
                                                     Executive Officer
   
  PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THIS AMENDMENT
NO. 2 TO THE REGISTRATION STATEMENT HAS BEEN SIGNED BY THE FOLLOWING PERSONS IN
THE CAPACITIES AND ON THE DATES INDICATED.     
 

<TABLE>
<CAPTION>
            SIGNATURE AND TITLE                                DATE
            -------------------                                ----
<S>                                         <C>
          /s/ John F. Grundhofer
- -------------------------------------------
            John F. Grundhofer,                          February 11, 1994
   Chairman, President, Chief Executive
                  Officer
and Director (principal executive officer)
            /s/ Richard A. Zona
- -------------------------------------------
              Richard A. Zona,                           February 11, 1994
 Vice Chairman and Chief Financial Officer
       (principal financial officer)
            /s/ Susan E. Lester
- -------------------------------------------
              Susan E. Lester,                           February 11, 1994
  Executive Vice President and Controller
      (principal accounting officer)
            Coleman Bloomfield*
- -------------------------------------------
       Coleman Bloomfield, Director                      February 11, 1994
 
- -------------------------------------------
          Roger L. Hale, Director
              John H. Kareken*
- -------------------------------------------
         John H. Kareken, Director                       February 11, 1994
            Richard L. Knowlton*
- -------------------------------------------
       Richard L. Knowlton, Director                     February 11, 1994
             Kenneth A. Macke*
- -------------------------------------------
        Kenneth A. Macke, Director                       February 11, 1994
</TABLE>

 
 
                                      II-2

<PAGE>
 

<TABLE>
<CAPTION>
            SIGNATURE AND TITLE                                DATE
            -------------------                                ----
<S>                                         <C>
             Thomas F. Madison*
- -------------------------------------------
        Thomas F. Madison, Director                      February 11, 1994
             Marilyn C. Nelson*
- -------------------------------------------
        Marilyn C. Nelson, Director                      February 11, 1994
          Will F. Nicholson, Jr.*
- -------------------------------------------
     Will F. Nicholson, Jr., Director                    February 11, 1994
             Nicholas R. Petry*
- -------------------------------------------
        Nicholas R. Petry, Director                      February 11, 1994
            Edward J. Phillips*
- -------------------------------------------
       Edward J. Phillips, Director                      February 11, 1994
              James J. Renier*
- -------------------------------------------
         James J. Renier, Director                       February 11, 1994
 
- -------------------------------------------
        S. Walter Richey, Director
            Richard L. Robinson*
- -------------------------------------------
       Richard L. Robinson, Director                     February 11, 1994
             Richard L. Schall*
- -------------------------------------------
        Richard L. Schall, Director                      February 11, 1994
             Lyle E. Schroeder*
- -------------------------------------------
        Lyle E. Schroeder, Director                      February 11, 1994
</TABLE>

 
          /s/ Susan E. Lester
*By__________________________________
           Susan E. Lester,
    Pro se and as Attorney-in-Fact
 
                                      II-3

<PAGE>
 

                                 EXHIBIT INDEX
 

<TABLE>
<CAPTION>
 EXHIBIT                           DESCRIPTION                            PAGE
 -------                           -----------                            ----
 <C>     <S>                                                              <C>
 23.3    Consent of Ernst & Young (relating to financial statements of
          First Bank System, Inc. and Colorado National Bankshares,
          Inc.)
 23.4    Consent of Price Waterhouse (relating to financial statements
          of Boulevard Bancorp, Inc.)
 23.5    Consent of Deloitte & Touche (relating to financial statements
          of Western Capital Investment Corporation)
</TABLE>






<PAGE>
                                                                    Exhibit 23.3

                        CONSENT OF INDEPENDENT AUDITORS

We consent to the reference to our firm under the caption "Experts" and to the
use of our report dated January 20, 1993, except for Notes C and I, as to which 
the date is May 28, 1993, with respect to the supplemental consolidated 
financial statements in Amendment No. 1 to the Registration Statement (Form S-4 
No. 33-51383) and related Prospectus of First Bank System, Inc. for the 
registration of 7,169,565 shares of its common stock.

                                           Ernst & Young

Minneapolis, Minnesota 
February 7, 1994





<PAGE>
                                                                    EXHIBIT 23.4



                       CONSENT OF INDEPENDENT ACCOUNTANT

We hereby consent to the use in the Propectus constituting part of Amendment 
No. 1 to the Registration Statement on Form S-4 of First Bank System, Inc. of
our report dated January 21, 1993, relating to the financial statements of
Boulevard Bancorp Inc., which appears in such Prospectus. We also consent to
the reference to us under the heading "Experts" in such Prospectus.


  /s/ PRICE WATERHOUSE
- ----------------------------
      PRICE WATERHOUSE


Chicago, Illinois
February 10, 1994







<PAGE>
                                                                    Exhibit 23.5








                         INDEPENDENT AUDITORS' CONSENT

We consent to the use in this Amendment No. 2 to Registration Statement No. 
33-51383, relating to the merger of First Bank System, Inc. and Boulevard 
Bancorp, Inc. on Form S-4, of our report dated January 30, 1992 relating to the 
financial statements of Western Capital Investment Corporation included in the 
Current Report on Form 8-K dated July 29, 1993 of First Bank System, Inc.


                                           Deloitte & Touche



DELOITTE & TOUCHE
Denver, Colorado

February 4, 1994



Leaving?

By selecting Continue, you will leave U.S. Bank and enter a third-party Web site. U.S. Bank is not responsible for the content of, or products and services provided by Intuit, nor does it guarantee the system availability or accuracy of information contained in the site. This Web site is not controlled by U.S. Bank. Please note that the third party site may have privacy and information security policies that differ from those of U.S. Bank.