Fifteen S/S children with severe SCD were transplanted with marrow from HLA identical siblings. All developed frequent (> 3/y) vaso-occlusive crises (VOC) associated with recurrent acute chest syndrome episodes (n = 10), osteitis (n = 3), osteonecrosis (n = 3), strokes (n = 3) or frequent massive deglobulisation (n = 2). Two children undergone splenectomy, two were chelated and two had an erythroid allo-immunization. Ethnic origins were from various countries in Africa (n = 11), North-Africa (n = 3) or West Indies (n = 1). At BMT, they were 2y 3m to 14y 9m old (mean: 8y 7m). Donors were AS (n = 11) or AA (n = 4). At first, various conditioning regimens were used consisting of busulfan (BU) plus Cyclophosphamide (CY) at different doses: CY:200 mg/kg (n = 13) or 260 mg/kg (n = 2); BU: 14 mg/kg (n = 1), 16 mg/kg (n = 9), > 16 mg/kg (n = 5); one patient received also TLI and the last two anti-thymoglobulin (ATG): 20 mg/kg. GVHD prophylaxis was CSA alone (n = 4) or CSA plus short-term MTX (n = 11). Median follow-up is 28 months (5 m to 53 m). All patients had an engraftment (d12 to d32) with a stable total chimerism in 10/14 patients. In the 4 others, partial chimerism was observed: one patient had a early and progressive rejection of his graft but is doing very well (35 m follow-up) without any manifestation of SCD, with a high stable 22% Hb F level.(ABSTRACT TRUNCATED AT 250 WORDS)