Persons in drug treatment with drug dependence were interviewed with the NIMH Diagnostic Interview Schedule to ascertain DSM-III-R disorders. Lifetime prevalence rates were 64% for alcohol dependence, 44% for antisocial personality disorder (ASPD), 39% for phobic disorders, 24% for major depression, 12% for dysthymia, 10% for generalized anxiety disorder, 3% for panic disorder, 3% for mania, 3% for obsessive compulsive disorder, 2% for bulimia, 1% for schizophrenia, and 1% for anorexia. When stratified by race and age, significant main effects were seen, but there were no significant interactions except in “any non-substance disorder” and in the mean number of non-substance use disorders. Caucasians had a higher mean number of drug dependence disorders and higher overall rates of “any other” disorder than African-Americans, and Caucasians and males had higher mean numbers of non-substance use disorders than African-Americans and females, respectively. This was related to rates of alcohol, cannabis, and hallucinogen dependence, and ASPD rates that were higher among men than women and higher among Caucasian respondents than African-American for alcohol, cannabis, hallucinogen, opiate and sedative dependence, major depression, dysthymia, and generalized anxiety disorder. In contrast, women had higher rates than men of amphetamine dependence, phobic disorder, major depression, dysthymia, panic disorder, obsessive compulsive disorder, and mania. African-Americans had higher rates than Caucasians of amphetamine, cocaine, and phencyclidine dependence, but for no comorbid disorders were the rates higher among African-Americans than Caucasians. The differences according to gender in rates of disorders among substance dependent persons are consistent with the results of general population surveys, but the differences in rates according to race are in contrast to these same community surveys. Limitations in the utility of the concept of race as a valid category diminish the generalizability of the findings; however, one possible explanation is differential treatment seeking in African-American and Caucasian populations that would result in the differences seen.