While the importance of measuring the performance of the information systems function (ISF) is well recognized, no comprehensive instrument exists to assess the ISF’s performance. This research develops a theoretical model of the ISF’ s performance based on existing research. The proposed model consists of three dimensions: systems performance, information effectiveness, and service performance. Based on the model, an instrument is developed to capture the perceptions of various IS user constituency groups. Therefore, in addition to validating the ISF performance instrument, this research also attempts to empirically differentiate IS users into parsimonious groups and to compare the differences in ISF performance assessments by the various constituencies.