Polycythemia vera is a blood disorder in which bone marrow makes too many red blood cells. Polycythemia vera also may result in production of too many of the other types of blood cells, white blood cells and platelets. But it's the excess red blood cells that thicken blood and cause most of the concerns associated with polycythemia vera. Polycythemia vera, also called primary polycythemia, is rare and usually develops slowly. Person may have it for years without noticing signs or symptoms. Often, polycythemia vera is found during a blood test done for some other reason. In general, this is a disease of middle and older age. Without treatment, polycythemia vera can be life-threatening. However, with proper medical care, many people experience few problems related to this disease. Carries increased risks of thrombosis, hemorrhage, myelofibrosis, and acute leukemia. Diagnosis is strongly associated with the presence of the JAK2V617F mutation, although this mutation is not specific for polycythemia vera. Treatment is based on stratification for risk of thrombosis, but includes low-dose aspirin and phlebotomy for most patients. High-risk patients also receive cytoreductive therapy. Ongoing and future studies will be required to further define disease etiology and appropriate therapy.