The present study examined the association of paternal alcoholism with early adolescent boys' school adjustment and substance use, and its moderation by paternal absence, controlling for parents' socioeconomic resources. A community sample of 653 urban, low socioeconomic status (SES) families from Montreal, Canada, was assessed and information collected from parents, teachers, and adolescents' self-reports, and school records. Paternal alcoholism was significantly associated with boys' lower academic performance, lower grades, higher frequency of tobacco, marijuana and hard drugs use, of getting drunk, and using a variety of hard drugs. However, the separation from the alcoholic father represented a significant factor of moderation in regard to boys' substance use: Sons of alcoholic fathers living with their dad in intact families were more likely to use tobacco and marijuana, to get drunk, and to use a variety of hard drugs than their peers not living with their alcoholic father, whether in single-mother or stepfamilies.