To study the characteristic of peripheral blood, bone marrow and JAK2V617F mutation status of essential thrombocythemia patients in National Hematology and Blood Transfusion. Patient and method: a descriptive study carry out 59 patients with essential thrombocythemia according to WHO 2008 criteria was diagnosed and treated in NIHBT from 01/2010 to 11/2011. Result and conclusion: mean age is 59 (26-85), male/female ratio is 0.51/1, incidence is high in the age over 60. Mean platelet count is 1453 + or - 476 x 10 exponent 9 /L. Bone marrow showed proliferation of megakaryocytes (91.5 percent) with abnormal shape. JAK2V617F was found in 52.5 percent of the patients. Patients with mutation have Hb and platelet count higher than the others (P0.05).