Background.The results of renal transplantation in obese recipients have been controversial, with some reports finding increased morbidity prohibitive and others finding increased morbidity acceptable. We attempted to determine whether obese patients in extreme excess of their ideal body weight should undergo transplantation.Methods.The study population included 127 obese (body mass index >30 kg/m2) patients who were compared with a matched nonobese control group (body mass index <27 kg/m2) of 127 recipients with similar demographics. There were no significant differences between the groups according to donor source, recipient race or sex, retransplants, transplant percent reactive antibodies, cause of renal failure, or hypertension. However, significantly more obese patients had a pretransplant history of angina (11.2% vs. 3.2%,P=0.02) or a previous myocardial infarction (5.6% vs. 0.8%,P=0.04).Results.The mean follow-up was 58.9±40 (range 3-170) months. Nonobese patients enjoyed a significantly (P=0.0002) greater patient survival (89% vs. 67%) at 5 years and suffered only about half the number of deaths (25 vs. 46) during the period of observation. Cardiac disease was the leading cause of death (39.1%) in the obese group. Patient death had a major impact on graft survival because there were no differences between the groups when death with graft function was censored from the analysis. There were no significant differences between the groups in delayed graft function, acute rejection, chronic rejection, length of hospital stay, operative blood loss, or mean serum creatinine up to 5 years. However, obese patients experienced significantly (P=0.0001) more complications per patient (3.3 vs. 2.2) and a greater incidence (P=0.0003) of posttransplant diabetes (12% vs. 2%). Similar cyclosporine blood levels were observed in obese recipients even though they were receiving 0.75-2 mg/kg/day less cyclosporine than the nonobese recipients.Conclusions.Outcome differences in obese renal transplant patients were primarily due to a higher mortality resulting from cardiac events. Obesity seems to have little effect on immunologic events, long-term graft function, or cyclosporine delivery. Aggressive pretransplant screening for ischemic heart disease is essential to identify an especially high-risk subgroup of obese patients. Although it would seem prudent to recommend weight reduction <30 kg/m2to all patients before transplant, these data suggest that obese patients with a history of cardiac disease should not be transplanted until weight reduction has been accomplished.