We have previously reported that kidney transplant recipients with enzyme-linked immunoabsorbent assay-reactive human leukocyte antigen (HLA) class I and II antibodies are at an increased risk for graft failure. To determine whether positivity for both classes of HLA antibodies before transplantation can serve as an indicator for identification of high-risk patients, the impact of preformed HLA antibodies on graft survival was analyzed in a new series of 5315 kidney transplantations performed between 2000 and 2008. In line with our previous findings, 121 first transplant recipients positive for both HLA class I and II antibodies by enzyme-linked immunoabsorbent assay had a poor 2-year graft survival rate of 76.5% +/- 4.0%, compared with a rate of 87.5% +/- 0.5% in 4175 recipients who were negative for both antibody classes (log-rank p < 0.001). Good survival rates of 82.7% +/- 3.2% and 86.1% +/- 2.7%, respectively, were observed in 149 HLA class I-positive/class II-negative recipients and in 183 HLA class I-negative/class II-positive recipients. Importantly, graft survival was good in HLA class I-positive and class II-positive patients when they received a kidney with a 0-1 HLA-A+B+DR mismatch. These data confirm our previous observation that kidney transplant recipients who simultaneously possess HLA class I and II antibodies in their pretransplantation serum are at increased risk for graft failure and require special attention.