Nucleophosmin (NPM1), encoded by the NPM1 gene localized at chromosome 5q35, is a multifunctional nucleo-cytoplasmic shuttling protein that is predominantly localized in the nucleoli. Acute myeloid leukemia (AML) is a clonal disease of hematopoietic progenitor cells, leading to increased numbers of blasts in the blood and/or bone marrow with concurrent suppression of normal hematopoiesis. AML is rapidly being recognized as a heterogeneous disease, with up to 55% of adult cases having nonrandom chromosomal aberrations, which can generally be detected by conventional karyotyping. Cytogenetically normal-AML is less frequent in children than in adults, and accounts for ±20 to 25% of childhood AML cases.