Mutations of nucleophosmin gene (NPM1) are known to be related to good prognosis in AML patients lacking FLT3 internal tandem duplication (FLT3-ITD). Recently, NPM1 mutations other than type A were reported, but their clinical significance is not well known. Retrospective medical record review of 106 de novo AML patients lacking FLT3-ITD, who received induction chemotherapy from three centers in Korea between 1997 and 2007, was performed. Direct sequencing of NPM1 and RT-PCR for FLT3-ITD was performed on genomic DNA derived from blood samples of patients before induction chemotherapy for detection of mutations. NPM1 mutation was detected in 18 patients, where 13 were type A mutants and 5 were non-type A mutants. CR, CR1-D and OS was not different according to NPM1 mutational status overall. But, non-type A NPM1 mutation was related to shorter CR1-D when compared with NPM1 wild types and NPM1 type A mutation (p = 0.004). OS was shorter in non-type A mutants when compared with NPM1 wild-type patients and NPM1 type A mutants (p = 0.001). The type of mutation of NPM1 is important for prognosis in de novo AML lacking FLT3-ITD. Non-A type NPM1 mutation is a poor prognostic factor.