This retrospective analysis of cytomegalovirus (CMV)-seropositive adult transplant recipients showed that CMV antigenemia occurred after transplantation in 10/10 (100%) recipients of unrelated cord blood, 17/39 (43%) recipients of a related matched donor graft, 16/23 (79%) recipients of an unrelated matched donor graft, and 8/12 (67%) recipients of a mismatched related donor graft. These results suggest that unrelated cord blood transplantation itself may be correlated with a high incidence of CMV reactivation.