The ASI was introduced in 1979 as a structured interview designed to assess the severity of addiction-related problems that often confront substance misusers. It was developed to meet the need for a standardized instrument capable of assessing clients, identifying treatment needs, and measuring improvement after treatment. The ASI takes approximately 35 minutes to complete and is designed to be administered by a trained interviewer. This study took a systematic sample of 23 detoxification clients during May and June 1991 who had been interviewed by the research staff before their third day in detoxification. Clients were approached again before their sixth day in residence by a different interviewer and were told that the researchers needed to clarify some ambiguous answers provided during the initial interview. Approximately 70 percent of the study sample were males and 30 percent were females. The primary measures of reliability were the kappa coefficient for categorical items and the intraclass correlation coefficient for continuous items. The concurrent validity of the instrument was assessed by using selected questions from each major section along with the corresponding composite measures. Preliminary evidence supports previous findings regarding the reliability and validity of the ASI among homeless substance misusers. Analyses of individual items show that they perform as well as or better than many other inventories previously tested in diverse populations. The authors caution that study results should be viewed with caution due to the small sample size and the sampling frame from which the respondents were drawn. 7 tables and 27 references