In order to estimate rates and identify risk factors for assaults on employees of a state psychiatric hospital, we examined workers' compensation claims, hospital-recorded incident reports, and data collected in a survey of ward staff. Results revealed 13.8 workers' compensation claims due to assault per 100 employees per year. Assaults were responsible for 60% of total claims. Incident reports revealed 35 injuries due to assault per 100 employees per year. Survey data revealed 415 injuries due to assault per 100 employees per year. Of the respondents, 73% reported at least a minor injury during the past year. Assault management training in the past year was associated with less severe injuries. Working in isolation, the occupation of mental health technician, and working on the geriatric-medical hospital unit were associated with more severe injuries during the past year. Assaults on staff in psychiatric hospitals represent a significant and underrecognized occupational hazard.