We present updated results of a multicenter collaborative investigation of bone marrow transplantation for sickle cell disease. Between September 1991 and April 1997, thirty-four children less than 16 years of age with severe sickle cell disease received marrow allografts from HLA-identical siblings. Indications for transplantation included a history of stroke (n = 17), recurrent acute chest syndrome or sickle pulmonary disease (n = 10), and recurrent vaso-occlusive crises (n = 7). Twenty-one patients received regular red blood cell (RBC) transfusions to prevent complications of sickle cell disease. Patients were prepared for transplantation with busulfan, cyclophosphamide, and antithymocyte globulin or CAMPATH (Cambridge Pathology) antibody. Thirty-two of the 34 patients survived, with a median follow-up of 26.5 months (range, 0.2-66.9 months); and 28 patients demonstrated stable engraftment of donor hematopoietic cells. Graft rejection or recurrence of sickle cell disease occurred in four patients, and two patients died of intracranial hemorrhage or graft-vs.-host disease. In the group of 34 children with symptoms of advanced sickle cell disease, current Kaplan-Meier estimates of survival and event-free survival are 93% and 79%, respectively.