An audit of unplanned returns by patients to the Accident and Emergency Department was carried out recently in Toa Payoh Hospital. This was done for a period of eleven months for the year 1994. A total of 166 unplanned patient returns were studied. We analysed the reasons for their return, whether there were any differences between the diagnoses made initially and at the return visit, and the outcome of these return visits. It was found that more than two-thirds of patients (72.3%) returned because of a failure to improve from their initial condition even after treatment given by the Emergency Department doctors. The six most common illnesses for which there were failure to improve were asthma, epigastric pains (including gastritis and peptic ulcer disease), gastroenteritis and food poisoning, renal and ureteric colic, minor head injury and backache. Another 14.5% of patients were found to have wrong or missed diagnoses at the initial visit, the two most important of which were appendicitis and bleeding from the gastrointestinal tract. It is hoped that such an audit will serve to identify areas for improvement in patient care. It can also be a useful tool for measuring and improving the performance of individual Emergency Room doctors, or a group of doctors.