The objective of this study was to identify biologic parameters that were associated with either exceptionally good or poor outcome in childhood acute myeloid leukemia (AML). Among the children with AML who entered Children's Cancer Group trial 213, 498 patients without Down syndrome or acute promyelocytic leukemia (APL) comprise the basis for this report. Univariate comparisons of the proportion of patients attaining complete remission after induction (CR) indicate that, at diagnosis, male gender, low platelet count (< or =20 000/microl), hepatomegaly, myelodysplastic syndrome (MDS), French-American- British (FAB) category M5, high (>15%) bone marrow (BM) blasts on day 14 of the first course of induction, and +8 are associated with lower CR rates, while abnormal 16 is associated with a higher CR rate. Multivariate analysis suggests high platelet count at diagnosis (>20 000/microl), absence of hepatomegaly, < or =15% day 14 BM blast percentage, and abnormal 16 are independent prognostic factors associated with better CR. Univariate analysis demonstrated a significant favorable relationship between platelet count at diagnosis (>20 000/microl), absence of hepatomegaly, low percentage of BM blasts (< or =15%), and abnormal 16 with overall survival. Absence of hepatomegaly, < or =15% day 14 BM blast percentage, and abnormal 16 were determined to be independent prognostic factors associated with better survival.