The fathers had a diagnosis of abuse or dependence on at least one drug other than alcohol or nicotine, although the latter drugs could be comorbid diagnoses. Fathers and sons were assessed using a variety of instruments. The data were analyzed by means of a structural equation path analysis. Results revealed that the joint influence of a paternal history of substance abuse and difficult temperament in fathers and sons influenced family and interpersonal processes that, in turn, influenced the developmental trajectory of the child toward deviant peer affiliations. The full model explained 50 percent of the sons' Peer Delinquency Scale scores. Findings indicated that primary prevention initiatives that take into account the effect of temperament on parent-child relationships may help improve the quality of family functioning and thus reduce the likelihood of the child's disengagement from the family to deviant peer affiliations at an early age. In addition, temperament counseling may also help redirect a child on a deviant developmental trajectory to more normative peer affiliations and psychosocial adjustment. Figures, tables, and 70 references (Author abstract modified)