This report examines the prevalence of personality disorders among hospitalized alcoholics and polydrug addicts and the extent and nature of the overlap between different axis II disorders. Subjects were 178 alcoholics admitted to a diagnostic unit of an addiction treatment institute and 86 polydrug addicts admitted to the therapeutic community of the same institute. Substance abuse was diagnosed according to DSM-III-R, and patients were assessed with the Structured Interview for DSM-III Personality Disorders (SIDP). In the alcohol group, 78% of the patients had at least one personality disorder and the average number of personality disorders was 1.8 per patient. In the polydrug group, 91% of the patients met criteria for at least one personality disorder and the average number of personality disorders was 4.0 per patient. No single "addictive personality" emerged. These findings raise questions about the validity and usefulness of the distinction between axis I and axis II disorders in patients with substance use disorders, and do not lend support to the validity of the categorical classification of personality pathology.