Use of allogeneic BMTs continues to increase. During the 33-year period between 1955 and 1987, more than 20,000 patients received allogeneic BMTs; more than 50% of these were performed in the 3 years, 1985 through 1987. Transplants are effective therapy for leukemia and other hematologic diseases. They are the treatment of choice for aplastic anemia and chronic myelogenous leukemia, those who fail conventional therapy for acute leukemia, and a variety of immune deficiency disorders. Successful application of BMT is limited by complications such as graft failure, GvHD and interstitial pneumonia, and, until recently, the requirement for an HLA-identical sibling donor. In the past few years, an increasing number of transplants was performed using HLA partially matched related or unrelated donors, with some success. The development of posttransplant complications can often be predicted by risk factor assessment. In this report, current data from the IBMTR are summarized and several risk factors affecting outcome identified.