Essential thrombocythemia is a rare myeloproliferative disorder in pediatrics. This myeloproliferative disorder is charactherized by thrombocytosis and hyperplasia of megakaryocytes in the bone marrow. Other cell lines are not involved. JAK2V617F mutation has been identified in approximately half the patients with this disorder. We describe a 12-year-old boy with essential throbocythemia. The patient had a persistent thrombocytosis over 600x10(9) /L and the time of diagnosis, his platelet count ranged between 900x10(9)and 2150x10(9)/L. Megakaryocytes in the bone marrow were increased in number. The chromosomal analysis was normal and bcr/abl rearrangement was negative. He remained asymptomatic throughout the follow-up period.