We undertook a retrospective survey of assaultive behavior in 140 psychiatric inpatient research volunteers who had not previously responded well to neuroleptic treatment. Forty-one of 97 patients with schizophrenia became assaultive during their hospitalization, whereas only four of 43 patients with other diagnoses became assaultive (p less than .0001). Most assaults were not a significant threat to the attacked person, but a small number were highly dangerous. Assaultive patients were significantly younger, and a greater proportion had a previous history of violence, compared with nonassaultive patients. A previous history of violent behavior was linked to more previous hospitalizations, indicating that such behavior might be associated with a poor prognosis.