The research reported in this article investigated the psychometric characteristics of the Independent Living Skills Survey (ILSS), a comprehensive, objective, performance-focused, easy-to-administer measure of the basic functional living skills of individuals with severe and persistent mental illness (SPMI). Two versions were developed, one for informants and one for self-report. Data from three research projects were analyzed to determine the versions' internal consistency, stability, interrater reliability, sensitivity to the effects of skills training, and concurrent and predictive validity. The results indicated that the two versions have acceptable psychometric characteristics, and suggestions are offered for their use in planning individualized treatment, evaluating programmatic services, and determining eligibility for benefits.