We performed a prospective study in our teaching hospital to determine the demand for a High Dependency Unit where none had existed before. An admission criteria protocol was designed for medical and surgical patients and this was used in an intense surveillance of 22 acute wards over 2 weeks. It was predicted that a high dependency unit of eight beds would operate to capacity 50% of the time. An analysis of this type over a short period of time using similar admission criteria could be used to assist in the prediction of the necessary size of a High Dependency Unit facility in any hospital.