Data from 3113 patients receiving HLA-identical sibling bone marrow transplants for leukemia were analysed to determine the time course of the major causes of treatment failure. The median interval from transplant to onset of acute graft-versus-host disease (GVHD) was 17 days, interstitial pneumonitis 63 days, and chronic GVHD 111 days. The median interval from transplant to relapse was 3.3 months for patients transplanted in relapse of acute leukemia or blast phase of chronic myelogenous leukemia (CML), 6.4 months when transplants were performed in second or subsequent remission of acute leukemia or accelerated phase of CML, and 7.8 months for patients transplanted during first remission of acute leukemia or while in the first chronic phase of CML. Shorter intervals from transplant to onset of interstitial pneumonitis or chronic GVHD were associated with a significantly lower probability of 2-year survival. The temporal relationships between these complications are displayed graphically and demonstrate the overlapping and competing causes of death following allogeneic bone marrow transplantation.