‘Prescription-event monitoring’ (PEM) is one of two national systems of post-marketing surveillance in operation in Britain. It identified 22 065 patients who had received NHS prescriptions for alprazolam, and data available on 10 895 of these were analysed. The main reasons for treatment with alprazolam were anxiety and depression. The patients provided 3360 patient-years of treatment and 7540 patient-years of follow-up. No serious events clearly associated with treatment were recorded. The main events reported during treatment, albeit infrequently, were drowsiness and depression, although depression is more likely to be due to the disorder being treated than to the drug. Some of the other alleged unwanted effects of alprazolam in published reports were not encountered. Since PEM is unable to determine the dependence potential of alprazolam, further evaluation of this problem is called for.