In this study, the relationship between the use of various substances, selected psychosocial characteristics, and violence was examined. Groups of subjects in treatment for a primary problem with cocaine (n=300), cannabis (n=128), alcohol (n=110), other drugs (33), tobacco (n=249) or gambling (n=199) completed a self-administered questionnaire. The questionnaire included questions on various psychosocial scales (i.e., aggressive personality, chronic stress, sleep problems, impulsivity, disrespect for the law and social supports), frequency of drug and alcohol use, and violence in the past year. For the univariate analyses, all of the drug and psychosocial variables were significantly related to violence. In the multivariate analyses, frequency of cocaine and alcohol use, disrespect for the law, aggressive personality, age and sex were significantly related to violence. The findings point to multi-causal explanations; however, both alcohol and cocaine use appear to play a significant role in explaining violence.