There were 294 children with acute myelogenous leukemia (AML) entered into the German AML Berlin, Frankfurt, and Münster hospitals (BFM) 78 and 83 studies. Thirty (10%) died as a result of hemorrhage and/or leukostasis prior to or in the first 12 days of therapy. The risk of early death due to hemorrhage and/or leukostasis is significantly greater when certain features are initially present: acute monocytic leukemia (French-American-British [FAB] M5), hyperleukocytosis (greater than or equal to 100,000/microliter), and extramedullary organ involvement (P less than 0.001). The risk increases sharply when these factors exist in combination: 72% mortality with FAB M5 and hyperleukocytosis, and 43% with FAB M5 and extramedullary organ involvement. In 11 patients leukostasis alone or in combination with hemorrhage was probably the cause of death during the first 3 days after diagnosis. All 11 children presented with hyperleukocytosis and were classified as monocytic subtype FAB M4 or M5. After induction, a close temporal association between rapid blast reduction and occurrence of fatal hemorrhage was established in five patients. Thrombocytopenic hemorrhages were controllable and, therefore, responsible for death only in exceptional cases. It is difficult to avoid these early fatal complications with current therapeutic measures. Early exchange transfusion together with special supportive care may be useful.