The present study is a random, systematic study of 900 homeless subjects in St. Louis that describes violence in their lives, both in terms of victimization, by specific violent traumatic events, and victimizing with recognized aggressive behaviors. Many subjects had experienced a traumatic event, and post-traumatic stress disorder was very common. Substance abuse and other Axis I disorders were associated with a history of a traumatic event. The majority of men and a substantial proportion of women also had a history of physically aggressive behaviors, often beginning in childhood. Aggressive adult behavior was associated with substance abuse and major depression. The aggressive behaviors usually predated homelessness, and about half continued after the individual had become homeless. Therefore, it is seen that violence is very much a part of the lives of the homeless, and it seems to be part of a broader picture of problems associated with risk for and experience of homelessness.