Participants in the clinical trial and the present study were 161 juvenile offenders meeting diagnostic criteria for substance use disorders and their families. Measures of youth delinquency and substance use as well as measures of family- and peer-related risk factors were obtained at three points during a 12-month period. Results showed that the relative effectiveness of JDC and the evidence-based treatments was likely due, at least in part, to the capacity of these interventions to alter well-established family (e.g., parent supervision) and peer (e.g., association with deviant peers) risk factors for antisocial behavior in adolescents. Implications of the findings for further improvements in the effectiveness of JDCs are discussed. (Published Abstract)