Mutations in nucleophosmin (NPM) exon 12 and the resulting delocalization of NPM into the cytoplasm are the most specific and frequent cellular events in acute myeloid leukemia patients (AML) with normal karyotype. Cytoplasmatic NPM (NPMc+) is associated with responsiveness to chemotherapy and better prognosis. The activation of nuclear factor-κB (NF-κB) has been demonstrated to occur in a subset of AML patients and is thought to induce resistance to many chemotherapeutical agents. In this study, we demonstrate the increased in vitro sensitivity of NPMc+ cells to chemotherapeutical agents and their reduced NF-κB activity. Furthermore, we provide evidence of the interaction between NPMc+ and NF-κB in the cytoplasm, resulting in the sequestration and inactivation of NF-κB. The cytosolic localization and consequent inactivation of NF-κB justifies the reduced NF-κB DNA-binding activity observed in NPMc+ patients. These data, taken together, may provide a possible explanation for the increased rate of chemosensitivity observed among the NPMc+ patients.