In a study examining the efficacy of an aerobic exercise program for adults with chronic psychiatric disabilities, the hypothesis that certain aspects of psychological well being would improve as fitness levels increased was tested. Using a quasi-experimental non-equivalent control group design, 37 adults with severe psychiatric disabilities participated in a structured aerobic exercise program that met three times a week for 30 minutes over 15–20 weeks. Psychological and physiological assessments occurred at five different, but equal points in time. Upon completion of the exercise phase, individuals participated in a follow-up period matching the exercise phase in duration. Significant positive changes were seen in both physical and psychological variables, indicating the potential of physical fitness as a rehabilitation intervention for persons with a psychiatric disability.