Polycythemia vera (PV) is a chronic myeloproliferative disorder due to a haematopoietic stem cell's clonal proliferation. PV is also characterized by independency or hyper sensibility of haematopoietic progenitors to several cytokine as erythropoietin. This acquired disorder is often associated with thrombocytosis, leukocytosis and splenomegaly. Generally, diagnosis remains easy, based on basic clinical and biological abnormalities. Sometimes, positive diagnosis required more sophisticated tests as assay of endogenous erythroid colony, erythropoietin blood level and bone marrow biopsy. Usually natural history of disease remains long with a good quality of life. In some cases complications occur: mainly thrombosis and late myeloid metaplasia with myelofibrosis and acute leukemia. Therapeutic approachs remain complex and difficult to optimize based up on age and disease severity. Treatment searchs for reducing hyper viscosity complications and for avoiding therapeutic induced leukemia.