We have sought to unravel the molecular biology of a female patient who in 1985 at the age of 55 was diagnosed with a chronic myeloproliferative neoplasm (MPN) and in whom overt acute myeloid leukemia (AML) developed in 2005. To this end, DNA and RNA (extracted from either paraffin‐embedded bone marrow (BM) or from BM and/or peripheral blood stored in an RNA/DNA‐preserving buffer) were analyzed by qPCR and by capillary gel electrophoresis of PCR products. We found the patient to be JAK2‐V617F mutation positive throughout the course of disease, while a mutation of the nucleophosmin (NPM1) gene emerged at AML diagnosis and relapse. The 20‐yr lag phase between the polycythemia vera and the AML adds indirect evidence to the growing realization that the leukemic transformation in patients with MPN occurs from in a JAK2 wild‐type stem cell.