The Addiction Severity Index (ASI) is a widely used interview among substance-dependent populations in treatment. Its value as a treatment planning and evaluation tool has been diminished by the lack of comparative data from nonclinical samples. The present study included four scales from the ASI collected on samples of adult subscribers to a large health maintenance organization (HMO) in northern California, as well as an adult clinical sample from the same geographic region with the same HMO insurance, thereby offering informative contrasts. Interviews (N = 9,398) of non-alcohol-dependent or abuse adults from a random sample of members of a large HMO were analyzed. We collected complete ASI data on the alcohol, drug, medical, and psychiatric composite scales and partial data on the employment scale. A sample of 327 adult members of the same HMO from one of the counties included in the survey, who were admitted to treatment for alcohol and/or drug addiction, was administered the same ASI items at treatment admission. Analyses compare problem severities in the two samples by age and gender. The general membership reported some problems in most of the ASI problem areas, although at levels of severity that were typically far below those seen in the clinical sample. General membership and clinical samples were somewhat similar in medical status and in employment. As expected, alcohol, drug, and psychiatric status were much more severe in the clinical sample. The data from the HMO general membership sample provide one potential comparison group against which to judge the severity of problems presented by drug- and alcohol-dependent patients at treatment admission and at posttreatment follow-up. The authors discuss the implications for treatment planning and the evaluation of treatment outcome.