This pilot study addressed the problem of patients' assaults on staff at a Norwegian psychiatric university hospital. The questionnaire-based study had a retrospective design, and involved a random sample of staff (n = 85). It revealed that 100% of the nursing staff and 60.9% of the therapists (doctors, psychologists, and social workers) had been physically assaulted by patients at least once during their careers at the hospital. Most of the assaults did not result in sick leave, and could as such be classified as not serious. There were no significant differences in the number of assaults on male and female staff or between staff in the emergency, intermediary, rehabilitation and psycho-geriatric wards. The staff responded that they believed male patients were more violent and threatening than female patients, although a majority had been assaulted more frequently by female than by male patients. Assault was the reason most frequently given for physically restraining patients, and most of the staff did not believe that physically restraining patients reduced their chances of recovery. The study suggests that patients' assaults on staff in Norwegian psychiatric hospitals is an important problem, which needs further attention.