The results of 20 total hip and knee arthroplasties performed in patients with morbid obesity who were treated with bariatric surgery before arthroplasty are reviewed. Bariatric surgery was successful in reducing the Quetelet ratio (weight in kilogram divided by height in square meters) of patients from a mean of 49 kg/m(2) (range, 38-56 kg/m(2)) to a mean of 29 kg/m(2) (range, 25-32 kg/m(2)). The average time from bariatric surgery to arthroplasty was 23 months (range, 7-65 months). The cumulative Knee Society score had improved significantly from a mean of 103.6 (range, 45-165) before arthroplasty to a mean of 148.9 (range, 66-185) at final follow-up in 12 knees undergoing total knee arthroplasty (P<.01). The Harris hip score also had increased significantly from a prearthroplasty mean of 40 (range, 25-55) to 67.5 (range, 50-95) at final follow-up in 8 hips receiving total hip arthroplasties (P<.05). All but 1 patient with continuing patellofemoral pain were satisfied with the result of the arthroplasty at final follow-up. One hip was revised at 5 years for aseptic loosening of the femoral component; no knee revisions were required. All other prostheses were stable with no evidence of radiographic loosening or wear at final surveillance. Morbidly obese individuals, with severe degenerative joint disease, who are considered unsuitable for arthroplasty because of excess weight should be considered for bariatric surgery. Total joint arthroplasty after surgical treatment of obesity has an excellent outcome with an acceptable complication rate.