A 5-year-old boy with severe aplastic anemia failed to respond to cyclosporine (CYA), prednisolone and antilymphocyte globulin (ALG). No suitable sibling marrow donor was available, but an HLA-matched unrelated donor was identified. The patient was conditioned with cyclophosphamide (CY), 50 mg/kg/day for 4 days, total nodal irradiation (8 Gy), and ALG 30 mg/kg/day for 3 days. GVHD prophylaxis consisted of daily CYA, methotrexate (MTX) and ALG. The patient failed to achieve sustained engraftment. He was reconditioned with high-dose prednisolone and anti-T lymphocyte monoclonal antibody OKT3. The boy was reinfused with the same donor marrow on day 0 (+49/first BMT). No GVHD prophylaxis was given the second time. He received G-CSF on days 0 to +20 after the second transplant. Full engraftment was achieved on day +16 (+65). However, on day +31 (80) he developed a biopsy-proven B cell lymphoproliferative disorder (BLPD). After the OKT3 administration was stopped and treatment with ganciclovir and high-dose immunoglobulin was initiated, the BLPD resolved and the patient was discharged on day +50 (99). He is currently well with a functioning graft 266 (305) days posttransplant, with no sign of GVHD.