A group of 114 patients undergoing total hip and knee arthroplasty were evaluated to assess the effect of total joint arthroplasty on quality of life, as measured by the SF-36 Health Status Questionnaire, and to determine the predictive relationship between preoperative and postoperative scores. A highly significant improvement was seen comparing preoperative with postoperative scores at 2 years for physical function, social function, physical role function, emotional role function, mental health, energy, and pain. Despite a significant change in health status (P < or = .001), no change was seen in the patient's health perception (P = .61). Regression analysis failed to indicate a predictive relationship between preoperative and postoperative scores for any scale. Total joint arthroplasty dramatically improves the quality of life and function of patients afflicted with arthritis; however, because of the poor ability of the SF-36 to predict postoperative improvement on an individual basis, it cannot be used alone to determine treatment selection.