Transformation of polycythemia vera to chronic myelogenous leukemia is a rare event. We report 2 women with long-standing polycythemia vera who developed chronic myelogenous leukemia. Both patients had no BCR/ABL1 fusion at the time of polycythemia vera diagnosis but were positive for the fusion at chronic myelogenous leukemia onset. Most patients with polycythemia vera have JAK2(V617F) mutation. Analysis of an archival bone marrow aspirate sample from 1 patient showed a heterozygous mutation status. The blood and bone marrow samples from the other patient showed the presence of homozygous JAK2(V617F) mutation and BCR/ABL1 fusion. The possible pathogenesis of such an event is discussed in the light of current literature.