A male infant with reticular dysgenesis received a bone-marrow transplant from his HLA-identical brother. Severe graft-versus-host disease developed but he responded to high-dose methylprednisolone. 3 years after grafting, the child is thriving with full haematological reconstitution and normal cell-mediated and humoral immunity. This is the first report of the survival beyond 17 weeks of a child with reticular dysgenesis.