Externalising behaviours, including the personality characteristics of behavioural undercontrol (BU), represent one of several genetically influenced domains that impact on the alcoholism risk. Because genes explain only about 60% of the vulnerability toward alcohol use disorders (AUDs), an optimal understanding of how such behaviours affect the risk requires evaluation of their impact in the context of additional influences. Few studies have addressed this question regarding BU among relatively well-functioning adults. This paper presents results from testing a BU-based mediational model of risk in men from the San Diego Prospective Study. Structured research instruments were used with 430 adult Caucasian males to evaluate the performance of BU in predicting AUDs at the 15-year follow-up using Pearson product-moment correlations among domains and an AMOS-based structural equation model (SEM). While both the family history of AUDs (FHalc) and BU predicted alcohol-related outcome, BU by itself did not mediate the relationship of the FH to alcohol disorders. The impact of BU on alcohol problems was mediated by alcohol expectancies, peer drinking and by coping. The SEM explained 42% of the variance for AUDs. The current results indicate that BU contributed to the risk for alcohol-related problems, even among more highly functional subjects and after excluding the impact of the antisocial personality disorder, but by itself did not mediate the relationship of FH to outcome in these subjects.