A review of studies on violence by psychiatric in-patients is presented. Violence in various settings has been studied and a few general conclusions emerge. The assailant is commonly a young schizophrenic. Only few patients are repeatedly violent. Persistently violent schizophrenics have been shown to have neurological impairments. Violence usually occurs in crowded, unstructured settings. There is no agreed definition of assaults and how they should be graded. Although violence is common it rarely leads to serious physical consequences. Victims are most often nursing staff. Some staff and patients are assaulted more often than others. Violence is difficult to predict. Ways of preventing assaultive behaviour are discussed. After considering some problems with existing studies, areas for further study are suggested.