To investigate the effects of increased weight and body mass index (BMI) on total knee arthroplasty (TKA) survivorship and on functional outcomes and quality of life following revision TKA, a prospective cohort study of 291 consecutive revision TKA patients was performed. Average patient BMI was 32.3 +/- 7.7, and 57% of patients were obese (BMI > or = 30). The obese group was not significantly different from the nonobese group regarding reasons for prosthesis failure; however, they were more likely to experience certain comorbidities. Body mass index and weight were both significant predictors of survivorship of primary TKA (regression coefficient BMI = -1.852, P = .004; regression coefficient weight = -0.405, P = .000) in multivariate regression. At 6-month follow-up, improvement of Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) stiffness, WOMAC difficulty of function, and Knee Society Score (KSS) function scales at 6 months after revision TKA was significantly lower (at the 0.001 level, two tailed) in patients with higher BMI, weight, or both. In regression analysis, BMI was a significant predictor of Short Form-36, WOMAC difficulty of function, and KSS. Weight and BMI have deleterious effects on the longevity of primary TKA and functional and quality of life outcomes following revision TKA. These findings indicate a need for more effective management of these patients.