OBJECTIVE The study was performed to determine the incidence, outcome and preventability of adverse events (AE) in an ED. METHODS The Quality in Australian Health Care Study methodology, modified to the ED, was utilized. Case histories of patients presenting to a tertiary hospital ED were screened for events. Events detected were classified, using a 104-item data collection instrument, entered on Excel and analysed statistically using MINITAB. RESULTS A total of 5345 patients presented during the study period. Three thousand three hundred and thirty-two patients completed full evaluation and comprised the study population. One hundred and ninety-four events were detected. Except where specified, events with management causation < or = 3 were excluded. This excluded 24 events (12.4%) leaving 170 for analysis. Of patients suffering an event, 53.5% occurred prior ED attendance, 41.7% of AE occurred within the ED, and 4.7% had contributions from both. The overall event rate, detected by the screening process, was 5.1%, with an incident rate of 1.98% and AE rate of 3.12%. The ED AE rate was 1.0%. If only those with management causation = 1 are excluded, then the overall event rate was 5.52%, with an AE rate of 3.33%. Fifty-five per cent of events were judged to be preventable (preventability score > or = 3). Events resulting in death and disability were more likely to be preventable (P < or = 0.04). CONCLUSIONS In conclusion, the Quality in Australian Health Care Study methodology has been utilized to provide data on incidents and AE in an ED.