This article describes the Role Activity Performance Scale (RAPS) and presents data from a study of its reliability and validity. The RAPS evaluates an individual’s functional level, using 12 subscales that represent a range of life roles. It was developed as an instrument for evaluating the impact of occupational therapy and other treatment modalities on the functioning of psychiatric patients. It is also useful in the diagnostic, treatment, and discharge planning processes. Validity and interrater reliability testing involved a sample of 30 patients in two major diagnostic groups. Interrater correlations for subscales and total scores were above .80 and statistically significant. A comparison of the RAPS with other accepted psychosocial rating scales showed strong correlations in scores. The psychometric evidence from this preliminary study supports the continued development and use of the RAPS for both clinical and research purposes.