Isolated myeloid sarcoma (MS, i.e. acute myeloid leukemia without detectable bone marrow infiltration) is rare and most patients subsequently develop overt AML. We prospectively performed whole exome sequencing of uterine MS, concomitant morphologically normal bone marrow (BM) and subsequently developing AML from two women. Both patients harbored preleukemic clones in the morphologically normal BM, including DNMT3A mutations. In addition, recurrent mutations were identified in the NFE2 gene, a gene not previously associated with AML or isolated MS. Retrospective studies of further MS samples, twelve with and four without preceding or concomitant bone marrow AML, revealed NFE2 mutations in two additional cases, both with isolated MS and prior myeloid malignancies. We conclude that DNMT3A mutated preleukemia may predispose for the frequent bone marrow relapses following isolated MS and that recurrent NFE2 mutations may have a role in the development of isolated MS.