Background.Posttransplant lymphoproliferative disorder (PTLD) remains a difficult management issue; therefore, many studies focus on the identification of risk factors to allow for preventive strategies. We investigated risk factors for PTLD in the adult renal transplant setting.Methods.A single-center, matched case-control study design was used. Cases were identified from patients who underwent a first renal transplant between January 1, 1985, and December 1, 2001. Two controls were chosen per case, matched (±1 year) by date of transplant and graft survival. Clinical and demographic data were ascertained from medical records. Pretransplant serology for Epstein-Barr virus (EBV) and cytomegalovirus was confirmed on frozen, stored sera. Statistical analysis included univariate and multivariable examination of putative risk factors using conditional logistic regression.Results.Twenty cases of PTLD were identified, an incidence of 2.4%. Median time from transplant to diagnosis was 55 months (range, 3–168 months), with 16 cases of late-onset PTLD (>1 year posttransplant). The only significant risk in univariate analysis was EBV-negative status at transplant (risk ratio 6.0,P=0.03). In multivariable analysis, EBV-negative status remained significant (adjusted risk ratio 8.9,P=0.01). The risk related to EBV status held true when late cases were analyzed separately (adjusted risk ratio 7.1,P=0.03).Conclusions.Pretransplant EBV-seronegative status is a strong risk for development of PTLD in adult renal allograft recipients, even in late disease. These results indicate that primary infection with EBV may have a pathogenic role in some cases of late PTLD.