To explore if other genetic mutations coexist in AML cases with IDH mutations, we performed mutation analysis of various different genes, i.e. FLT3, NPM1, NRAS and AML1. IDH1 mutations were found to be most frequently accompanied by NPM1 mutations (74% of the cases; P < 0.001). The gene discussed is NPM1; the disease is acute myeloid leukemia.