Vaquez polycythemia (PV) is a myeloproliferative neoplasm resulting from clonal expansion of a pluripotent hematopoietic stem cell, causing proliferation of myeloid tissue predominantly in the erythrocyte lineage. It is characterized by an increase in total erythrocyte mass and hemoglobin without excessive stimulation by erythropoietin. Its incidence is low (2 to 3 cases per 100,000 inhabitants/year). The initial presentation is often pauci symptomatic. In some patients the occurrence of a thrombotic event or symptoms related to hyperviscosity syndrome leads to the diagnosis of PV.The discovery of the JAK2 V617F mutation has completely changed the diagnosis of PV and has allowed not only a better understanding of the pathophysiological mechanisms, but also the development of a targeted molecular therapy associated with an efficient molecular monitoring.