General hospital wards have to make provision not only for emergency cases but also for patients admitted from waiting lists. Admission of emergency cases and especially of short-stay emergencies use many of their beds and retards the admission of list cases. Short-stay emergencies do not require highly specialized treatment and it is wasteful of facilities in major units to reserve beds for them there. Such patients, however, must be admitted for surveillance or short-term treatment or even because of geographic or social considerations. Since 1958 a short-stay ward has been part of the Casualty Department of Aberdeen Royal Infirmary, and this paper describes fluctuations in the admission rate and number of beds occupied. It is interesting that the fluctuations can be very simply described mathematically. The random nature of emergency admissions makes this possible and there are no elective admissions to affect the situation. Our findings provide a method of predicting the number of beds actually required to allow for random fluctuations. The hospital centre for the north-eastern region of Scotland is in Aberdeen where there are Casualty Departments at the Royal Infirmary and at the Royal Aberdeen Hospital for Sick Children. The population served is approximately 250,000, and of that number about 190,000 live in the City of Aberdeen. The Casualty Department of the Aberdeen Royal Infirmary is situated at Woolmanhill about 2 miles from the main hospital at Foresterhill. It maintains a 24-hour service and is staffed by full-time Casualty Officers (one Registrar, one Junior Hospital Medical Officer, and three House Officers) with a Senior Casualty Officer of Senior Hospital Medical Officer