This study evaluated psychometric properties of the Addiction Severity Index (ASI) in 231 pathological gamblers. Internal consistency was similar to that reported in substance abusers, temporal stability was good, and convergent and discriminant validity was established with other indices of patient, collateral, and interviewer-rated reports. Predictive validity of most subscales was excellent when baseline composite scores were used to predict the utilization of relevant services or unemployment, probation/parole status, and bankruptcy one year later. Thus, the ASI may be a useful tool for assessing gambling and psychosocial problems in the growing population of treatment-seeking gamblers.