Many organizations have deployed system development methodologies in order to improve information systems development. Various factors influencing th e successful adoption of system development methodologies have been identified by numerous stud ies. However, a need was identified to evaluate the post-implementation efficiency of system developmen t methodologies. The aim of this paper is to present theoretical and empirical background for an evaluation model to measure the efficiency of a software development methodology after implementati on. A linear programming method called Data Envelopment Analysis was used to compare the applic ation of the Extreme Programming system development methodology in different organizations. According to the results of the analysis, it was possible to classify organizations’ use of Extreme Programming as efficient or inefficient. Recommendations could be made to increase efficiency of individual organizations that were classified as inefficient.