We report an unusual case of a symptomatic patient who initially had high hemoglobin and low serum erythropoietin levels, fitting a clinical diagnosis of polycythemia vera. However, after treatment with hydroxyurea and serial phlebotomies had been started, the patient developed hypereosinophilia, fitting the category of a myeloproliferative neoplasm with eosinophilia associated with the FIP1L1-PDGFRA gene fusion, as confirmed by molecular analysis. We discuss the clinical presentation, evolution, response to treatment, and pathogenetic implications of this case. © 2012 Elsevier Inc.