The intent of this National Institutes of Health–sponsored study was to compare a belatacept-based immunosuppressive regimen with a maintenance regimen of tacrolimus and mycophenolate. Nineteen primary, Epstein–Barr virus–immune renal transplant recipients with a negative cross-match were randomized to one of three groups. All patient groups received perioperative steroids and maintenance mycophenolate mofetil. Patients in groups 1 and 2 were induced with alemtuzumab and maintained on tacrolimus or belatacept, respectively. Patients in group 3 were induced with basiliximab, received 3 mo of tacrolimus, and maintained on belatacept. There was one death with a functioning allograft due to endocarditis (group 1). There were three graft losses due to vascular thrombosis (all group 2) and one graft loss due to glomerular disease (group 1). Biopsy-proven acute cellular rejection was more frequent in the belatacept-treated groups, with 10 treated episodes in seven participants compared with one episode in group 1; however, estimated GFR was similar between groups at week 52. There were no episodes of posttransplant lymphoproliferative disorder or opportunistic infections in any group. Protocol enrollment was halted prematurely because of a high rate of serious adverse events. Such negative outcomes pose challenges to clinical investigators, who ultimately must weigh the risks and benefits in randomized trials.