Langerhans' cell histiocytosis (LCH) is an uncommon disorder of childhood, formerly referred to histiocytosis X. A significant proportion of children with disseminated disease may undergo progression to a fatal outcome despite chemotherapy with single or multiple agents. Only six cases of LCH treated with BMT have been reported in the literature, including two cases of autologous BMT. Of them, only one was less than 14 years of age. We describe a 4-year-old child whose disseminated, refractory Langerhans' cell histiocytosis was not controlled by front-line monotherapy with etoposide, nor by rescue treatment with combined chemotherapy (vinblastine and etoposide) and immunotherapy (steroids and cyclosporine). Due to the high risk of fatal progressive disease, he underwent bone marrow transplantation from his HLA-identical sister who was heterozigous for beta-thalassemia. On day 24 after transplantation marrow reconstitution was evident, with WBC count 2.3 x 10(9)/L, neutrophil count > 0.5 x 10(9)/L, and platelet count 72 x 10(9)/L. Engraftment was demonstrated by PCR DNA analysis. The patient was discharged on day 25. After transplantation he experienced fever for 11 days and developed signs of grade I cutaneous and intestinal graft-versus-host disease, that was treated with methylprednisolone from days 11 to day 68 (1 mg/kg/day for 18 days, then tapered). He became transfusion independent on day 24; the hemoglobin value was 7.5 g/dL on day 54 and has remained > 10 g/dL since day 200. Features of heterozygous beta-thalassemia have been evident since then. Bone marrow aspirate was normal on days 25 and 94. At the time of this writing he remains in excellent condition, disease and treatment free, 25 months after transplantation. Although limited, current experience suggests that bone marrow transplantation has the potential to cure refractory Langerhans' cell histiocytosis.