Nucleophosmin (NPM1) mutations occur frequently in adult cytogenetically normal acute myeloid leukemia (CN-AML) and confer favorable outcome. We investigated the frequency and prognostic significance of NPM1 mutations in childhood AML (n=298), specifically focusing on the CN-AML subgroup (n=100). Mutations were found in 8.4%, and clustered significantly in the CN-AML subgroup (22%). No mutations were found in patients below the age of 3 years; in CN-AML, there was an increasing incidence above this age. In the overall group, NPM1 mutations conferred an independent favorable prognostic impact on event-free survival (5-year pEFS 66 vs 39%; P=0.02), which did not translate into a significantly better overall survival (5-year pOS 68 vs 56%; P=0.30). However, when the favorable cytogenetic subgroups [inv(16) and t(8;21)] were excluded from the NPM1 wild-type group, the difference in pOS was borderline statistically significant (68 vs 45%; P=0.07). In the CN-AML cohort, NPM1 mutations were an independent prognostic factor on pEFS (80 vs 39%; P=0.01), and pOS (85 vs 60%; P=0.06), which was not influenced by FLT3/ITD. However, in NPM1 wild-type CN-AML, FLT3/ITD-positive patients had a significantly worse outcome (pEFS 48 vs 18%; P<0.001). We conclude that NPM1 mutations confer a favorable prognosis in childhood AML and in CN-AML in particular.