Introduction: Studies addressing the utilization of post-transplant cyclophosphamide (CY) as graft-versus-host disease (GVHD) prophylaxis in allogeneic hemopoietic stem cell transplantation from matched sibling donors are limited and with controversial results. Chronic GVHD incidence necessitating systemic treatment is around 35% in peripheral blood stem cell transplantation (PBSCT) from human leukocyte antigen-matched sibling donors.Patients And Methods: In this study, high-dose CY was added to PBSCT aiming to reduce the incidence of GVHD to reach a lower figure compared with standard GVHD prophylaxis. Fifty-two patients with either benign or malignant hematologic disorders who underwent stem cell transplantation at Nasser Institute Hospital in Egypt from November 2017 to October 2018 were enrolled in this study. Fifty patients had fully human leukocyte antigen-matched siblings, whereas the remaining 2 patients had 1 locus class I mismatched donors. Pre-transplant conditioning regimen was fludarabine and busulfan (FLU/BU) in malignant cases (73.1%) and FLU/CY in benign hematologic disorders (26.9%) and 1 patient with hypocellular myelodysplastic syndrome. For GVHD prophylaxis, CY was given at a dose of 50 mg/kg/day on days 3 and 4 post-transplantation, and cyclosporine (CSA) starting day 5 in 96.1% of patients. For the 1-locus mismatched patients, both CSA and mycophenolate mofetil were administered starting day 5.Results: The 1-year incidence of acute GVHD (aGVHD) was 15.3% and for chronic GVHD (cGVHD) was 13.4%. Historical data of GVHD prophylaxis at our center using CSA and methotrexate showed an incidence of 37% for aGVHD and 33.9% for cGVHD.Conclusions: Post-transplant CY GVHD prophylaxis led to significantly less aGVHD (P = .03) and cGVHD (P = .04).