Two hundred twenty-two patients admitted to a geriatric psychiatry unit were surveyed for the commission of acts dangerous to others. Eighteen of these patients had used either guns or knives in acts of violence. Organic illness accounted for a minority of such acts, the majority having been perpetrated by patients with functional diagnoses of late paraphrenia, schizophrenia, or mania. The most dangerous patients were those who, in a clear sensorium, experienced paranoid delusions, hallucinations, or both, and believed that they were in danger of being attacked. One hundred twenty-one aggressive patients who did not use weapons against others were also identified. This group, which included a larger percentage of patients suffering from dementia, posed a much less serious threat to others than the violent group.