Immunosuppressive regimens that effectively prevent graft-versus-host disease (GVHD) after allogeneic blood or marrow transplantation (alloBMT) have been associated with an increased incidence of posttransplantation lymphoproliferative disorder (PTLD) in the first year after transplantation. We evaluated the incidence of PTLD associated with the use of high-dose, posttransplantation cyclophosphamide (PTCy) as GVHD prophylaxis. From 2000-2011, 785 adult alloBMT patients received PTCy as GVHD prophylaxis at the Johns Hopkins Hospital, including 313 who received PTCy as sole GVHD prophylaxis. HLA-haploidentical or unrelated donor grafts were used for 526 (67%) patients. There were no cases of PTLD in the first year after alloBMT. PTLD is rare after alloBMT using PTCy, even in high-risk alternative donor transplants.