As filed with the Securities and Exchange Commission on April 27, 1998
                              Registration No. 333-
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-4
             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                      TRANSACTION SYSTEMS ARCHITECTS, INC.
             (Exact name of registrant as specified in its charter)

                                    Delaware
         (State or other jurisdiction of incorporation or organization)

                                      7372
            (Primary Standard Industrial Classification Code Number)

                                   47-0772104
                      (I.R.S. Employer Identification No.)

                             224 South 108th Avenue
                              Omaha, Nebraska 68154
                                 (402) 334-5101
   (Address, including ZIP Code, and telephone number, including area code, of
                    registrant's principal executive offices)

                          William E. Fisher, President
                      Transaction Systems Architects, Inc.
                             224 South 108th Avenue
                              Omaha, Nebraska 68154
                                 (402) 334-5101
 (Name, address, including ZIP Code, and telephone number, including area code,
                            of agent for service)

            It is requested that copies of communications be sent to:
                                Neal A. Klegerman
                                Baker & McKenzie
                              One Prudential Plaza
                             Chicago, Illinois 60601

Approximate  date of  commencement  of proposed  sale of the  securities  to the
public:  As soon as practicable  after the effective  date of this  Registration
Statement.  

If 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. [ ]

If this Form is filed to register additional securities for an offering pursuant
to Rule 462(b) under the  Securities  Act,  check the following box and list the
Securities  Act  registration   statement   number  of  the  earlier   effective
registration statement for the same offering. [X] 333-24279

If this Form is a  post-effective  amendment filed pursuant to Rule 462(d) under
the  Securities  Act,  check  the  following  box and  list the  Securities  Act
registration  statement number of the earlier effective  registration  statement
for the same offering. [ ]

If any of the  securities  being  registered on this Form are to be offered on a
delayed or continuous  basis  pursuant to Rule 415 under the  Securities  Act of
1933, other than securities offered only in connection with dividend or interest
reinvestment plans, check the following box. [X]



                         Calculation of Registration Fee
- --------------------------- ----------------------- ----------------------- ------------------------ ----------------------- Proposed Title of each class Proposed maximum of securities to be Amount to be maximum offering aggregate offering Amount of registered registered price per unit (1) price (1) registration fee - --------------------------- ----------------------- ----------------------- ------------------------ ----------------------- =========================== ======================= ======================= ======================== ======================= Class A Common Stock, par 224,264 shares $38.875 $8,718,263 $2.575 value $.005 per share =========================== ======================= ======================= ======================== =======================
(1) Estimated solely for the purpose of calculating the registration fee pursuant to Rule 457(c) promulgated under the Securities Act of 1933, as amended, based upon the average of the high and low prices of the Class A Common Stock on April 20, 1998, as reported on The Nasdaq National Market. _______________ This Registration Statement is being filed pursuant to Rule 462(b) under the Securities Act of 1933, as amended. The contents of the Registration Statement on Form S-4 (File No. 333-24279), previously filed by the Registrant and declared effective by the Commission on April 10, 1997, are incorporated herein by reference. The required opinions and consents are listed on the Exhibit Index attached hereto and filed herewith. SIGNATURES Pursuant to the requirements of the Securities Act, the registrant has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Omaha, State of Nebraska, on April 27, 1998. TRANSACTION SYSTEMS ARCHITECTS, INC. By: /s/ Gregory J. Duman -------------------- Gregory J. Duman Chief Financial Officer Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed by the following persons in the capacities and on the dates indicated. Name Title Date ---- ----- ---- * Director and President April 27, 1998 - ----------------- (Principal Executive Officer) William E. Fisher /s/ Gregory J. Duman Chief Financial Officer April 27, 1998 - -------------------- (Principal Financial Officer) Gregory J. Duman * Vice President April 27, 1998 - ----------------- (Principal Accounting Officer) Dwight G. Hanson * Director April 27, 1998 - ----------------- David C. Russell * Director April 27, 1998 - ----------------- Jim D. Kever * Director April 27, 1998 - ----------------- Promod Haque * Director April 27, 1998 - ----------------- Charles E. Noell, III * Director April 27, 1998 - ---------------- Larry G. Fendley /s/ Gregory J. Duman April 27, 1998 - --------------------- *Gregory J. Duman as Attorney-In-Fact Pursuant to Power of Attorney Granted in Registration Statement No. 333-24279 ================================================================================ EXHIBIT INDEX ================================================================================ Exhibit Number Description - ------- ---------------------------------------------------------------------- 5.01 Opinion of Baker & McKenzie 23.01 Consent of Independent Public Accountants 23.02 Consent of Baker & McKenzie (included in opinion filed as Exhibit 5.01) 24.01 Power of Attorney (contained in Signature Page to Registration Statement on Form S-4 (File No. 333-24279) and incorporated herein by reference)


                                BAKER & McKENZIE
                                Attorneys at Law

                              One Prudential Plaza
                             130 East Randolph Drive
                             Chicago, Illinois 60601

                                 April 27, 1998


Board of Directors
Transaction Systems Architects, Inc.
224 South 108th Avenue
Omaha, Nebraska 68154

         Re:      Transaction Systems Architects, Inc. (the "Company")

Gentlemen:

     We have acted as your counsel in  connection  with the  registration,  on a
Registration  Statement on Form S-4 (the  "Registration  Statement")  under Rule
462(b) of the  Securities  Act of 1933,  as amended,  of an  additional  224,264
shares of the  Company's  Class A Common  Stock,  $.005 par value per share (the
"Stock"),  to be issued by the Company in connection  with an acquisition by the
Company. We have reviewed the Registration Statement, the charter and by-laws of
the Company,  corporate  proceedings  of the Board of Directors  relating to the
issuance of the shares of Stock, and such other documents, corporate records and
questions of law as we have deemed  necessary  to the  rendering of the opinions
expressed below.
        
     Based upon the foregoing,  we are of the opinion that the 224,264 shares of
Stock to be issued by the Company as described in the Registration Statement are
duly authorized and, when issued and paid for in the manner  contemplated in the
Registration  Statement,  will be legally issued,  fully paid and non-assessable
shares of Class A Common Stock of the Company.

     We hereby  consent to the  reference  to our firm under the caption  "Legal
Matters"  in the  prospectus  incorporated  by  reference  in  the  Registration
Statement and to the filing of this opinion as an exhibit thereto.

                                                              Very truly yours,


                                                              BAKER & McKENZIE



                  CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS

As independent  public  accountants,  we hereby consent to the  incorporation by
reference in this Form S-4  Registration  Statement of our reports dated October
30, 1997, included in Transaction  Systems  Architects,  Inc.'s Annual Report on
Form 10-K for the fiscal year ended September 30, 1997, and to all references to
our firm included in this Registration Statement.
  
                                                           ARTHUR ANDERSEN LLP

Omaha, Nebraska,
  April 27, 1998