Within certain industries there is an increasing prevalence toward computerizing work practices and mandating specific tasks performed using an Information System (IS). This trend is unlikely to diminish the need for stakeholders, involved in the implementation of an IS, to identify the determinants of successful use. Yet, to date, there is a paucity of research that has considered the issues specific to predicting and explaining user behavior in these situations. In this paper, we identify the relevant issues necessary for applying the technology acceptance model and the theory of planned behavior to the prediction and explanation of mandated IS usage, and we assess the value of these models to the task. The results of a longitudinal study conducted in a hospital setting are presented and we suggest the direction that future research might take.