The concurrent validity of the Addiction Severity Index (ASI), a new scale for assessing a range of clinical dimensions in drug and alcohol abusers, was evaluated in 204 opiate addicts applying for treatment. This study is the first independent validation study of this measure. The ASI subscales were found to have good concurrent validity with self-report measures in the areas of psychological problems, social adjustment problems, legal problems, and employment problems (r = .55 to .39). Drug abuse problems showed limited concurrent validity and medical problems were not concurrently assessed in our study. Addicts with psychiatric diagnoses beyond opiate abuse were effectively identified by the ASI, and depressed addicts were particularly well screened with a sensitivity of 89 per cent and a specificity of 67 per cent. A cluster analysis demonstrated that the six ASI scales could be used to discriminate depressed addicts, antisocial addicts, and addicts without psychiatric disorders. Thus, the ASI was demonstrated to be a potentially important evaluation instrument for opiate addicts.