One variant of substance-use disorder is characterized by behavioral disinhibition. In thisreport, we martial evidence for a model for the development of this variant. We hypothesize thatgenetic liability for this variant is reflected in a spectrum of risk indicators linked to the inabilityor unwillingness to inhibit behavioral impulses. Included in this spectrum are personality traitssuggesting low constraint, and externalizing psychopathology, including conduct, oppositionaldefiant, and attention-deficit disorder in children and antisocial personality disorder and behaviorin adults. We further hypothesize that these individual differences in behavioral disinhibition aremanifestations of underlying central nervous system processes associated with variouspsychophysiological anomalies, some of which may index genetic risk for substance abuse.Support for the model is derived from the analysis of findings from the Minnesota Twin FamilyStudy, an epidemiological investigation of approximately 2,700 adolescent twins and theirparents.