Three hundred seventy inpatient and outpatient substance abusers were divided according to presence and subtype of antisocial personality disorder (APD) into groups comparing: a) adult antisocial behavior (AAB) versus full APD; b) APD with low versus high sociopathy; c) APD with versus without lifetime depression; and d) APD with versus without other axis II disorders. Multivariate regression was used to predict the unique contribution to the variance in baseline and 12-month follow-up measures of substance use, psychiatric severity, and personality. The presence of comorbid axis II pathology was the strongest predictor of baseline severity in all three domains. APD substance abusers with lifetime depression exhibited greater baseline to follow-up reductions in psychiatric severity than those APD substance abusers without a history of depression. All APD subtypes improved over time with treatment, suggesting that this diagnosis does not necessarily indicate poor prognosis.