Exhibit 10.53

STOCK OPTION CANCELLATION AGREEMENT

         This Stock Option Cancellation Agreement is entered into as of August
30, 2002, by and between CSG SYSTEMS INTERNATIONAL, INC., a Delaware corporation
(the “Company”), and EDWARD C. NAFUS (“Grantee”).

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         The Company and Grantee hereby agree as follows:

         1.       In consideration of and in exchange for the award to Grantee
of 60,416 shares of the Common Stock of the Company as a Restricted Stock Award
pursuant to the 1996 Stock Incentive Plan of the Company, the terms and
conditions of such Restricted Stock Award being set forth in a Restricted Stock
Award Agreement dated as of August 30, 2002, between Grantee and the Company
entered into concurrently with this agreement (the “Award Agreement”), Grantee
hereby surrenders to the Company for cancellation all of the following Stock
Options previously granted to Grantee under the 1996 Stock Incentive Plan of the
Company (collectively, the Options”):

  (a)   Stock Option covering 80,000 shares of Common Stock granted on November
17, 1998;         (b)   Stock Option covering 25,000 shares of Common Stock
granted on January 7, 2000;         (c)   Stock Option covering 35,000 shares of
Common Stock granted on January 17, 2001;         (d)   Stock Option covering
37,500 shares of Common Stock granted on December 14, 2001; and         (e)  
Stock Option covering 37,500 shares of Common Stock granted on January 17, 2002.

         2.       The Options hereby are cancelled, effective as of August 30,
2002, and shall have no further force or effect; and Grantee shall have no
further rights of any kind under any of the Stock Option Agreements with the
Company which evidenced the grant of the Options.

         3.       This agreement shall be binding upon and inure to the benefit
of the Company and the Grantee and their respective heirs, personal
representatives, successors, and assigns.

         4.       The Company agrees to recommend to the Compensation Committee
of the Board of Directors of the Company that, not sooner than March 1, 2003,
such Committee grant new stock options to Grantee under the 1996 Stock Incentive
Plan of the Company. However,

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Grantee understands and acknowledges that such future grant, if any, and its
terms and the number of shares of Common Stock of the Company covered by any
such future grant are subject to all of the relevant terms and provisions of the
1996 Stock Incentive Plan of the Company and to the discretion of such
Committee.

         5.       Grantee agrees to and hereby does fully and forever release,
discharge, and waive any and all claims, complaints, causes of action, or
demands of whatever kind which Grantee now has or at any time hereafter may have
against the Company or against any of the Company’s subsidiaries, affiliates,
predecessors, and successors or against any of their respective past and present
directors, officers, and employees by reason of any event, matter, cause, or
thing which occurred on or prior to the date of this agreement arising out of,
involving, or related to the grant, ownership, or cancellation of the Options.
Notwithstanding the foregoing provisions of this Paragraph 5, Grantee does not
waive any rights which Grantee may have to require the issuance and delivery of
shares of the Common Stock of the Company pursuant to the Award Agreement.

         6.       This agreement and the Award Agreement constitute the entire
agreement of the Company and Grantee with respect to the subject matter of this
agreement, and there are no other or further promises, understandings, or
agreements between the Company and Grantee with respect to the Common Stock of
the Company or any existing or future options to acquire shares of such Common
Stock.

         7.       This agreement shall be governed by and construed in
accordance with the laws of Delaware.

         IN WITNESS WHEREOF, the Company and Grantee have executed this Stock
Option Cancellation Agreement as of the date first above written.

  COMPANY:

CSG SYSTEMS INTERNATIONAL, INC.,
a Delaware corporation
  By: 
/s/ NEAL C. HANSEN

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      Chairman of the Board and Chief
Executive Officer

    GRANTEE:
   
/s/ EDWARD C. NAFUS

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      Edward C. Nafus

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