Lifetime and 6-month prevalence rates of DIS/DSM-III diagnoses were determined in 152 Ss in a clinical detoxification center; 80% of the sample had at least one recent psychiatric disorder in addition to substance abuse. The three most prevalent disorders, antisocial personality (ASP), depressive disorder, and anxiety-related disorder, were commonly diagnosed in combination. Nearly one half of the Ss with antisocial personality also had a depressive or an anxiety-related disorder, but only the latter two were significantly interrelated. Ss with ASP were demographically distinct and had a longer history of drug use compared with other Ss. Recent drug use was not associated with any of the diagnostic groups. Interactions between psychopathology and drug use are discussed as are strengths and limitations of the diagnostic instruments.