There is evidence that the psychological attribute of perceived self-efficacy plays a role in mediating health outcomes for persons with chronic arthritis who take the Arthritis Self-Management Course. An instrument to measure perceived self-efficacy was developed through consultation with patients and physicians and through study of 4 groups of patients. Tests of construct and concurrent validity and of reliability showed that the instrument met appropriate standards. Health outcomes and self-efficacy scores improved during the Arthritis Self-Management Course, and the improvements were correlated.