The clinical course of polycythemia vera (PV) and essential thrombocythemia (ET) is characterized by an increased incidence of thrombotic and hemorrhagic complications and an inherent tendency to progress into myelofibrosis or acute myeloid leukemia. Major predictors of vascular events are increasing age and previous thrombosis. Myelosuppressive drugs can reduce the rate of thromboses and hemorrhages, but there is concern that their use accelerates the rate of leukemic transformation. Thus, a risk-oriented management strategy is recommended. Low-risk patients with PV should be treated with phlebotomy and low-dose aspirin, whereas those with ET can be left untreated. Cytotoxic agents are recommended in high-risk cases and hydroxyurea is the drug of choice in most patients. Interferon alpha or anagrelide could be considered in selected young patients or as second-line therapy in those refractory or intolerant of hydroxyurea. The recent identification of JAK2V617F mutation in a substantial proportion of patients with PV and ET raises new questions regarding both risk classification and management, but additional studies on these issues are required.