About 50,000 hematopoietic stem cell transplantations are performed yearly, primarily for malignancies. Use of this therapy increased dramatically over the past 30 years due to its proven and potential efficacy in diverse diseases, better understanding of appropriate timing of transplantation and patient selection, and greater availability of allogeneic donors. The International Bone Marrow Transplant Registry (IBMTR) and the Autologous Blood and Marrow Transplant Registry (ABMTR) collect data on consecutive allogeneic and autologous transplants, respectively, in more than 400 participating centers worldwide. The IBMTR/ABMTR database contains information on more than 120,000 transplant recipients. Among 11,347 patients transplanted in 101 IBMTR/ABMTR research centers in North America during 1995-1997, 66% received autologous transplants, 24% related-donor transplants, and 10% unrelated-donor transplants. More than 90% of transplantations were for malignant disease, with more than half of these done in patients with advanced disease. Of the recipients, 70% were younger than 50 years. Posttransplant survivals varied substantially by disease, transplant type, recipient age, and disease status at transplantation. IBMTR/ABMTR data provide an important tool for assessing transplant use and outcome, identifying prognostic factors for transplant outcomes, evaluating new transplant therapies, comparing transplant and nontransplant therapies, evaluating late transplant complications, and planning prospective phase II and III clinical trials.