Fourteen S/S children with severe SCD were transplanted with marrow from HLA identical siblings. All developed frequent (> 4/y) vasoocclusive crises (VOC) and 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, 2 were chelated and 2 had erythroid allo-immunization. Ethnic origins were from various countries in Africa (n:10), 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:3). At first, various conditioning regimens were used consisting of busulfan (BU) plus Cyclophosphamide (CY) at different doses: CY:200 mg/kg (n:12) or 260 mg/kg (n:2); BU:14 mg/kg (n:1), 16 mg/kg (n:9), > 16 mg/kg (n:4); 1 patient received also TLI and one other antithymoglobulin (ATG): 20 mg/kg. GVHD prophylaxis was CSA alone (n:4) or CSA plus short-term MTX (n:10). Median follow-up was 23 months (8 m. to 48 m.). All patients had an engraftment (d13 to d32) with a stable total chimerism in 10/14 patients who are cured. In the 4 others, partial chimerism was observed: one patient had a early and progressive rejection of his graft but is doing very well (28 m. follow-up) without any manifestation of SCD, with a high stable 22% Hb F level. One patient developed an aplastic anaemia 15 m after BMT: a second BMT was achieved 21 m after the first one with engraftment and total chimerism. Two patients have a relatively stable partial chimerism with still undergoing CSA therapy (11 m. and 23 m. follow-up).(ABSTRACT TRUNCATED AT 250 WORDS)