The developmental timing of paternal substance use disorder (SUD) offset on internalizing and externalizing problem behaviors was examined in prepubertal sons. Analyses revealed a significant main effect of the developmental timing of SUD offset on both internalizing and externalizing problems. No differences were found between sons of control-subject fathers and SUD+ fathers whose offsets occurred before the son's sixth birthday. However, when paternal SUD extended beyond the boys' sixth year, significant increases in internalizing and externalizing problem behaviors were found. The results suggest the importance of early parental SUD intervention in prevention of the intergenerational transmission of behavioral problems.