A register of violence incidents showed a progressive increase in in-patient violence from 1976 to 1984, followed by a slight decline to 1987. The case notes of all 137 in-patients committing assaults during 1982 were analysed and compared with those of matched controls. Violence was often repetitive. The most common victims were nurses and then patients. The violent patients were more likely to be schizophrenic, deluded and hallucinated, and to have been repeatedly admitted. The violent and control groups had similar backgrounds, and both showed high levels of social isolation and unemployment. Violence tended to be repetitive, and the violent patients were usually identifiable from previous aggressive and disturbed behaviour. There was a high proportion of Afro-Caribbean patients who tended to be younger, more psychotic, and more seriously violent. Afro-Caribbeans were particularly likely to be detained compulsorily and treated in a locked ward.