We report a 10-year-old boy with a severe form of immunodeficiency with hyper-IgM who underwent successful bone marrow transplantation with his HLA-matched sister as donor. Busulfan (20 mg/kg) and cyclophosphamide (200 mg/kg) were used as conditioning. The post-transplant course was uneventful. He is alive 25 months later with full hematological and immunological reconstitution.