We studied the association between explicit appropriateness criteria for total hip joint replacement (THR) and total knee replacement (TKR) with changes in health-related quality of life of patients undergoing these procedures.Prospective observational study of 1576 consecutive patients with diagnoses of osteoarthritis on waiting lists to undergo THR or TKR. Explicit appropriateness criteria using the RAND appropriateness method were applied. Patients completed 2 questionnaires that measured health-related quality of life, the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), before the procedure and 6 months afterward.Patients who were considered appropriate candidates for these procedures had greater improvements than those who were considered inappropriate candidates in all 3 WOMAC domains (pain, functional limitation, and stiffness; THR: 43.0, 40.6, and 40.4 vs 14.7, 19.1, and 15.9; TKR: 34.9, 32.5, and 30.2 vs 23.2, 18.9, and 17.1; P<.001 for all comparisons). Patients who underwent THR and were judged to be appropriate candidates had greater improvements in the physical function, role-physical, bodily pain, and social function domains of the SF-36 than those judged to be inappropriate candidates (34.4, 35.1, 33.1, and 26.6 vs 19.6, 9.2, 5.7, and 7.0; P = .04, P = .03, P < .001, and P < .001, respectively). Appropriate candidates for TKR demonstrated greater improvement in the social function domain of the SF-36 after the procedure than those deemed inappropriate candidates (19.9 vs 7.9; P = .004) but not in the other domains of functional status.These results suggest a direct relationship between explicit appropriateness criteria and better health-related quality-of-life outcomes after THR and TKR surgery. Our results support the use of these criteria for clinical guidelines or evaluation purposes.