Adverse events are a serious source of harm to patients and a large drain on the resources of healthcare providers. Retrospective studies have previously been carried out in the USA, Australia and the UK. In this study a prospective approach was employed, using similar methods to previous studies to detect the levels of adverse events over a period of one month. We also recorded the categories, causes and preventabilities of adverse events. We measured the degree of disability and the length of additional bed stay. Of the 537 patients treated in our department, 15 (2.8%) had adverse events; these patients were older than those who did not have adverse events, and were mainly emergency admissions. Most of the adverse events were operative and led to temporary disability. Overall, 139 extra bed stays were attributed to these adverse events. This report confirms the feasibility of conducting a prospective study of adverse events and of making preliminary estimates of their incidence and costs.