An 18-year-old boy with idiopathic severe aplastic anemia underwent unrelated bone marrow transplantation (BMT) from a 4/6 HLA-matched (mismatches in HLA-A and HLA-DRB1 loci) male donor after 9 years of treatment with cyclosporin A. After a preparative regimen consisting of FLU (25 mg/m2/day for 5 days), MEL (70mg/m2/day for 2 days), rabbit anti-thymocyte globulin (ATG) (1.25 mg/kg/day for 4 days), and TBI 2Gy, unrelated bone marrow cells (2.0 × 108/kg of mononuclear cells) were transfused with GVHD prophylaxis of TAC from day -1. The gene discussed is HLA-A; the disease is aplastic anemia.