This paper applies data from a family study of depression to assess patterns of comorbidity and co-transmission of alcoholism, anxiety disorder, and major depression. We found that all three disorders were strongly transmissible; however, alcoholism demonstrated the greatest degree of familial aggregation. The pairwise associations among depression, anxiety and alcoholism indicated that the traits are co-transmitted in families, especially depression and anxiety. Individual associations between traits (or comorbidity) were entirely explained by transmitted (perhaps genetic) agents, because the correlations between traits due to random environment were not significant. These findings have important implications for treatment, psychiatric nosology, and aetiological investigations of these conditions.