271 children with AML entered the cooperative studies BFM-78 (151 pat.) and BFM-83 (120 pat.) since Dec. 1, 1978. In the second study BFM-83 the 8-10 week intensive induction/consolidation therapy of study BFM-78 was preceded by an 8-day intensive therapy consisting of cytosine arabinoside, daunorubicin and VP-16. 10 children died prior to starting the protocol therapy from hemorrhage and/or leukostasis. 80% of the 261 protocol patients achieved a complete remission. 7% were early deaths by hemorrhage and/or leukostasis 3% died of other complications. 10% were partial or nonresponders. 54 relapses, 11 with CNS involvement have occurred in study BFM-78 after a follow up of 2.10-6.7 years (median 4.10 yrs.). The life table probabilities for event free survival (EFS) and event free interval (EFI) after 6.7 years are 37% (SD 4%) and 47% (SD 5%) respectively. The results of study BFM-83 after a follow up of 0.3-2.8 years (median 1.8 yrs.) are: 23 relapses, EFS 40% (SD 10%) and EFI 48% (SD 12%). So far, the overall results of both studies are nearly identical. The analyses of the prognostic factors show that initial hyperleukocytosis (greater than or equal to 100 X 10(3)/mm3) represents a high risk for early fatal hemorrhage and/or leukostasis, for nonresponse and for the incidence of relapses. Initial deaths caused by hemorrhage and/or leukostasis occur also significantly more often in patients with M5-subtype and extramedullary organ involvement. Additional strategies for achieving a better prognosis in high risk patients are necessary.