This study used classical test therapy to assess the psychometric properties of the Environmental Rating Scale (ERS), a measure specifically designed to assess the treatment programs in residential settings that serve individuals with autism. Results of the confirmatory factor analysis support the presence of a single factor represented by the total score. The reliability of the measure was demonstrated by assessments of the internal consistency, stability, and interrater reliability. Preliminary analysis of the validity of the ERS indicates that this measure discriminates between treatment settings designed specifically for individuals with autism and those designed for other populations of developmentally handicapped clients and family homes. The ERS was also significantly positively correlated with a measure of the caregiver's knowledge about autism and a visitor's global impression of the desirability of the setting as a place to live.