Because of growing concern about violence in health care in Australia, we reviewed the relevant data on incidents involving violence collected using the Australian Incident Monitoring System (AIMS). Among 42 338 incidents reported from 1 July 2000 to 30 June 2002, 3621 (9% of all incidents) involved patients and physical violence or violent verbal exchange; staff injury was reported in 5% of cases. The proportion was higher in emergency departments (16%, with frequent involvement of mental health problems or alcohol or drug intoxication) and mental health units (28%). Contributing factors include changes in our society and in mental health service provision. With the closure of public psychiatric hospitals in the past decade, more patients with mental illness are seeking care in public hospital emergency departments. AIMS analysis highlights the importance of understanding the contributing and precipitating factors in violent incidents, and supports a variety of preventive initiatives, including de-escalation training for staff; violence management plans; improved building design to protect staff and patients; and fast-tracking of patients with mental health problems as well as improved waiting times in public hospital emergency services. We recommend that a national system be developed to share and compare incident monitoring data, to monitor trends, and to facilitate learning and thinking at all levels - ward, department, hospital, state and national.