OBJECTIVE To describe the incidence and characteristics of aggressive behaviors in a group of institutionalized elderly. METHODS Retrospective survey. METHODS 350-bed, urban skilled nursing facility. METHODS All nursing home residents who had an incident report completed after an aggressive behavior. METHODS Examination of all incident reports of aggressive behavior for 1 year. RESULTS There were 94 reports of aggressive behaviors. Twenty-nine residents exhibited one aggressive behavior, 12 residents two, and six residents exhibited three or more aggressive behaviors. These six residents accounted for 44% of all events. The incidence of aggressive behavior was 0.27 per resident per year for the entire facility; on the Alzheimer's unit the incidence was 0.75 per resident per year. Sixty-two percent of the victims of aggressive behavior were other nursing home residents, 37% were employees, and 1% were visitors. The charts of the six residents with three or more aggressive behaviors were reviewed. These residents received trials of multiple scheduled psychotropic medications, often exhibited several additional agitated behaviors around the time of the attack, were at risk for psychiatric hospitalizations during the study period, and often were noted to have underlying acute medical illnesses near the time of the attack. CONCLUSIONS Approximately two aggressive behaviors per week occurred in a large nursing home. Residents and staff of Alzheimer's units have a higher risk of being victims of aggressive behavior. A small number of patients account for nearly half of the behaviors, even on the Alzheimer's unit. Aggressive behaviors may be clinical indicators of underlying acute medical illnesses.