The objective of the study was to learn how delusions, substance abuse, and violence are related. The sample was 90 hospitalized patients with adequate descriptions of mental status when violent. Data sources were risk assessment based on record review and patient and staff interviews. The data include history of violence and substance abuse, diagnosis, and demographic and legal status. Delusions were definitely or questionably present in 73.3 percent and absent in 26.7 percent of violent episodes; 83.5 percent of delusionally violent patients had a history of substance abuse. These results support the importance of substance abuse in relation to violence by psychiatric patients. Delusions alone were infrequently related to violence, but when present appeared almost always to drive the violent behavior.