The day hospital is one of a series of experiments in devising new psychiatric treatment settings. It has been a useful and productive development. The models created in different centres differ widely in their general applicability, their clinical usefulness, and their theoretical interest. The first day hospital was set up at the Allan Memorial Institute in 1946, and in 1958 was reorganized to provide services in combinations matched to the individual patients and readily varied as necessary. Coincidentally a re-examination of its social structure led to an activity program which produced marked changes. These changes not only remedied current difficulties operating the day hospital but also greatly extended its range of usefulness.