After allogeneic hematopoietic stem cell transplantation, risk factors for cytomegalovirus (CMV) reactivation include pretransplantation donor and recipient CMV serologic status and posttransplantation development of acute graft-vs-host disease (aGvHD). Human leukocyte antigen (HLA) allele type is an additional factor in CMV infection. The present study included 108 patients who received an allogeneic stem cell graft from an HLA-identical sibling between 1993 and 2004. All recipients and donors were typed for HLA-A, HLA-B, and HLA-DR alleles using serologic or molecular methods. All recipients received grafts because of a hematologic disease from HLA full-matched donors. In pretransplantation seropositive patients with aGvHD, no significant difference was observed in patients who developed CMV infection compared with those without CMV infection. Seropositive patients without aGvHD but with posttransplantation CMV infection demonstrated a higher incidence of HLA-A30, HL4-B40, and HLA-DRB1*15 compared with those without CMV infection. In conclusion, it seems that certain HLA alleles may have either a protective or predisposing role in CMV reactivation, which might be helpful in estimating the risk of aGvHD and designing individualized therapy.