It is hypothesized that accelerated sexual maturity in males results in deficient behavioral self-regulation that in turn results in a higher likelihood and severity of early involvement with psychoactive drugs and early onset of substance use disorder. This study tested the theory that sexual maturation and consequent personality development mediated, in part, parental contribution to children’s liability variations. Because it is well known that sex hormones play a role in self-regulation, this mediation hypothesis is plausible. Subjects of the study were members of the nuclear families participating in a family/high-risk study of substance use disorder (SUD) where probands were adult males with or without a DSM-III-R diagnosis of SUD who had a 10- to 12-year-old male child (females were added later). This took into account the fact that sons of substance abusing fathers had been shown to have a considerably higher risk of SUD than sons of nonaffected fathers. The results showed that the rate of sexual maturation in boys was significantly related to parental SUD, especially maternal SUD. The results of a structural equation model analysis were consistent with partial mediation of this relationship by sexual maturation, influencing sensation seeking, and a marker that was associated with the subsequent early onset of SUD. While the possible mechanisms for this relationship, including its mediation by family stress or biological factors have not been studied, this finding nevertheless points to a possible pathway of intergenerational transmission of SUD liability. This pathway includes the affect of the rate of reproductive development on behavior. Boys with early onset of puberty are more likely to engage in risky behaviors and a wider range of delinquent activities. Tables, figures, references