Accident and Emergency (A&E) departments are increasingly popular venues for primary care, causing a serious threat to healthcare quality. This paper reports the development of a comprehensive research method for identifying primary care patients attending A&E. Patients were randomly selected from the four A&E departments across different time periods and different regions in Hong Kong. The definition of GP cases was based on a retrospective record review conducted by a panel of emergency physicians using the standard laid down by the Hong Kong College of Family Physicians. The patients sampled were similar in sex and age distribution to A&E attendees for the whole territory. The level of GP cases was found to be 57 per cent, with a significantly higher proportion of patients in the younger age group. The high level of use reflects the lack of a well co-ordinated development of primary care services and interfacing with secondary care.