Background: C-KIT mutation and extramedullary infiltration highly occur in AML1-ETO-positive acute myeloid leukemia (AE-AML). Whether they having the same clinical significance in pediatric and adult patients remains unsure.  Procedure: Totally 75 pediatric and 98 adult patients with newly diagnosed AE-AML from 5 centers were included and analyzed. Results: The incidence of extramedullary leukemia (EML) (13.3% vs. 29.6%, P=0.008) and c-KIT mutations (12/68, 17.6% vs. 30/74, 40.5%, P=0.003) in pediatric patients were less than half compared to adult counterpart. The disease outcome including complete response (CR), disease-free survival (DFS) and overall survival (OS) was comparable between the two patient groups, when induction/consolidation regimens were taken into consideration. Based on multivariate analysis, EML was associated with a higher relapse and worse survival, and patients carrying c-KIT mutations showed a trend toward a worse prognosis. Grouping by age, the adverse effect of EML and c-KIT mutations on prognosis was only seen in adults but not children and was not affected by consolidation regimens. Conclusions: The occurrence of EML and c-KIT mutations was much less in pediatric than adult AE-AML. Both EML and c-KIT mutations adversely impacted the disease outcome in adult but not pediatric patients, suggesting the behavior of AML1-ETO fusion protein might be age-dependent.