We performed a one-year follow-up study of 266 alcoholics who had received extensive psychiatric assessment, including diagnosis with the National Institute of Mental Health Diagnostic Interview Schedule and DSM-III criteria, during their index treatment episode. The aims were to evaluate the relationship between additional DSM-III diagnoses in alcoholics and outcome at follow-up, assess the relative prognostic power of different ways of measuring psychopathology by comparing categorical DSM-III diagnoses and a global symptom severity measure, and assess whether ratings of psychopathology add to the prognostic power of an alcohol-dependence measure. While coexistent psychiatric diagnoses generally predicted poorer treatment outcome, there were significant interactions in the relationship between diagnoses and treatment outcome for men and women. For men, having an additional diagnosis of major depression, antisocial personality, or drug abuse was associated with poorer outcome. For women, having major depression was associated with a better outcome in drinking-related measures, while antisocial personality and drug abuse were associated with poorer prognosis. The value of determining psychiatric diagnosis was supported by covariance analyses that suggested that prognostic significance of specific disorders was not accounted for by general psychopathology or general dependence dimensions.