OBJECTIVE Although factors related to inpatient aggression have been extensively studied, there is relatively little specific information about violence in intensive care, so the authors decided to conduct their own research into the subject. METHODS The authors studied the behaviours of the small number of patients who are involved in most of the aggressive incidents in a psychiatric intensive care unit (PICU) over 15 months. RESULTS The study found that female patients were significantly more likely to be involved in aggressive incidents, but that most of these incidents involved self-harm. Patients with a diagnosis of schizophrenia were more likely to display violent behaviour than those from other diagnostic categories. Patients with a personality disorder were more likely to inflict violence against themselves. CONCLUSIONS The authors concluded that all the research on patient violence needs to be standardised to inform practice properly. Nurses need to be aware that relatively few patients are responsible for most of the violent incidents that occur.