Bone marrow transplantation is widely used to treat hematologic, immune, and genetic diseases. More than 9,500 transplants have been performed by 199 transplant teams worldwide; 162 are currently active. The annual rate of allogeneic bone marrow transplants now exceeds 2,500 plus more than 1,000 autotransplants annually. Transplantation is an effective therapy for acute leukemias; in some instances, it is the preferred treatment. In chronic myelogenous leukemia, aplastic anemia, and some genetic and immune diseases, bone marrow transplantation provides the only possibility for cure. Bone marrow transplantation remains investigational in many conditions and is associated with substantial problems such as GvHD, interstitial pneumonitis, and the requirement for an HLA-identical donor. Recently an increasing number of transplants have been performed using HLA partially or fully matched, related or unrelated donors with some success. The development of GvHD and interstitial pneumonitis can, to some extent, be predicted by risk-factor assessment. Although GvHD can be prevented by depleting T cells from the donor bone marrow, this is associated with an increased risk of graft rejection and leukemia relapse. Interstitial pneumonitis can be modified by prophylaxis with CMV-immune globulin and by the use of CMV-negative blood donors. In this report, we summarized data from the International Bone Marrow Transplant Registry concerning allogeneic bone marrow transplantation in man.