The Program Environment Scale (PES) was developed for use with clients of community-based programs for the severely mentally ill. It is intended to fill the gap in available tools for assessing clients' perceptions of program functioning as it affects their "quality of life" in a program. Formal pretests were conducted with 121 clients at 12 randomly selected programs near Washington, DC. The final field test used a revised form (29 domains; 129 items) with 221 clients in 22 programs selected randomly throughout the U.S., including Clubhouse, day treatment, psychosocial rehabilitation, and social club programs. Twenty-three subscales met at least five of eight psychometric criteria for internal consistency and discriminant validity. A 24th subscale was retained because of its substantive importance. Successful subscales cover program atmosphere and interactions (program cares about me, energy level, friendliness, openness, staff-client and client-client respect, reasonable rules, availability of positive physical contact, protection from bad touch, staff investment in their jobs, and confidentiality), client empowerment/staff-client equality (program and treatment empowerment, egalitarian space use), and service components (support for paid work, work importance, emergency access, family activities, housing, public benefits, community activities, medications, substance abuse, and continuity). Subscale validity is indicated by associations of specific service offerings with scores on scales measuring client perceptions of those services, and by an ability to differentiate among program models (i.e., Clubhouses, day treatment programs, and psychosocial rehabilitation programs look different from each other). Subscale scores were not influenced by client characteristics (gender, race, age, diagnosis, number of hospitalizations, length of time in program). The final scale has 97 items and takes about 25 minutes to complete. The PES succeeds in measuring different aspects of programs as clients perceive them. In the programs we visited, directors felt the PES covers the important things they want to know about how clients perceive their program. The PES should become a useful tool both for researchers interested in how client responses to programs may influence their therapeutic outcomes, and for practitioners interested in improving their clients' program experiences and/or increasing convergence of staff and client views of their program.