Within a 'whole system' approach to the management of acute medical referrals, many hospitals have introduced Medical Assessment Units (MAUs) to improve the care of acutely ill patients by assessing their need for hospital admission or discharge. This paper gives details of a research study designed to investigate the extent of MAU provision in the West Midlands Region, how these Units are organized and the nature of nursing roles within them. Results indicate that MAUs are organized and managed in different ways according to the likely length of patient stay. Likewise, nursing roles vary depending upon the context in which the nurses are working.