All children in Sweden who underwent bone marrow transplantation (BMT) with an HLA-identical sibling during a 5-year period were compared to those who were treated with chemotherapy and survived at least 3 months after remission. All patients were observed for more than 2 years after diagnosis or relapse. All 11 children with acute myeloid leukemia in first remission who underwent BMT survived compared to only 1 of 15 treated with chemotherapy (p less than 0.001). In children with acute lymphoblastic leukemia (ALL), those relapsing while on chemotherapy and treated with BMT in second to fourth remission (n = 16) had a 5-year survival of 43% compared to 16% for those treated with chemotherapy (n = 53, p less than 0.05). In children with ALL relapsing after cessation of therapy, 4-year survival was 33% for BMT (n = 6) and 55% for chemotherapy (n = 15), p = 0.05).