OBJECTIVE This study investigated the progression from conduct disorder to antisocial personality disorder among individuals treated for adolescent substance abuse. This issue is important because of the poor outcomes observed among individuals with antisocial pathology after treatment for alcohol and drug problems. The utility of factors assessed at the time of treatment in predicting progression to adult antisocial personality disorder was evaluated in the context of developmental models of antisocial behavior. METHODS This was a prospective longitudinal study of 137 substance-abusing adolescents (53 female and 84 male), whose average age was 15.9 years and who met the DSM-III-R criteria for conduct disorder. Consecutively admitted patients were recruited from two adolescent inpatient alcohol and drug treatment facilities. Participants were interviewed again 4 years after treatment. RESULTS Four years after treatment, 61% of the study group met the DSM-III-R criteria for antisocial personality disorder. Results of a logistic regression analysis indicated that onset of deviant behavior at or before age 10, a greater diversity of deviant behavior, and more extensive pre-treatment drug use best predicted progression to antisocial personality disorder. At 4-year follow-up, the subjects with an antisocial personality disorder diagnosis exhibited more involvement with alcohol and drugs and poorer functioning across important life domains than the subjects without antisocial personality disorder. CONCLUSIONS This study found a high rate of progression to antisocial personality disorder among substance-abusing adolescents and identified factors predictive of this progression. Careful assessment of conduct disorder history at the time of treatment may be valuable for treatment planning and intervention.