It is apparent from previous studies in clinical populations that there is a high comorbidity rate between alcoholism and other psychiatric diagnoses. However, this may simply be an expression of Berkson's bias (i.e., an increased tendency for persons with multiple diagnoses to seek and receive treatment and thus fall into study populations drawn from treatment sources). In this article, we use data from the Epidemiologic Catchment Area survey to examine the comorbidity between alcohol abuse and dependence, other substances of abuse and nonsubstance psychiatric disorders in a sample of approximately 20,000 persons drawn from the general population. We also examine the effect of comorbidity on psychiatric treatment. Every one of the psychiatric diagnoses we examined was more likely to occur in alcoholics than in nonalcoholics. Associations were particularly strong with antisocial personality disorder, other substance use and mania. The association between alcoholism and depressive disorders was positive but not very strong. The presence of other illnesses increased the likelihood of utilization of treatment services by alcoholics but did not increase the likelihood that drinking problems would be communicated to a doctor. The findings confirm prior studies of comorbidity in clinical samples and suggest the need for increased vigilance toward alcoholism by physicians.