An ontogenetic framework for elucidating the etiology of substance use disorders (SUD) requires identifying how individual traits and family contexts combine to increase risk for SUD outcomes. In this study, we examine individual traits in family context to identify processes that account for the relationship between fathers' SUD + status and sons' externalizing behaviors. Results obtained from SUD + (n = 89) and SUD - (n = 139) families show that fathers' abusive propensities toward their sons mediated the relationship between fathers' SUD + status and sons' externalizing behavior scale (EBS) scores 2 years later. Moreover, individual traits, family contextual variables and deviant peer affiliations accounted for 58% of the variance on sons' EBS scores. Also, high risk cluster (HRC) and low risk cluster (LRC) memberships were derived from cluster analyses of the continuous risk factor scores that predicted sons' EBS scores. Preliminary relative risk ratios show that sons classified into the HRC at age 10-12 were at greater risk for DSM-III-R conduct disorder and SUD outcomes at age 16 than sons assigned to the LRC, SUD + or SUD - groups. Implications for selected family-based prevention initiatives are presented.