In the course of social development, family influences seem to become partly internalized and transformed into personality characteristics that regulate behavior outside the family sphere. In a longitudinal study of 81 boys and their families, we hypothesized that individual differences in boys' self-restraint would serve as a mediator between family factors in preadolescence and sons' delinquent behavior 4 years later. Measures were derived from principal components analyses of multiple indices of each construct as assessed by multiple informants. As expected, parenting practices measured at both pre- and mid-adolescence predicted delinquent acts only indirectly via their association with boys' self-restraint. In addition, general family functioning at preadolescence, independent of other scores, predicted boys' levels of self-restraint 4 years later. There was no evidence that boys' self-restraint at preadolescence systematically affected the quality of parenting that they subsequently received. Parents' and families' role in children's development of self-regulatory skills may be a primary vehicle by which they ultimately influence adolescents' problem behaviors.