Essential thrombocytemia (ET) is a clonal myeloproliferative disorder of unknown cause, characterized by an increased number of apparently normal platelets. It has been related to a large number of mild ischemic complications, but rarely to acute stroke associated with documented large vessel thrombosis. We report the cases of 6 patients with acute ischemic stroke associated with ET (4 men and 2 women; mean age 61.7: range 49-78 years). The diagnosis of ET followed the onset of the stroke. The number of platelets was never greatly increased at the time of the stroke, and two patients presented no major risk factors for stroke. The involvement of the posterior circulation was observed in three patients, that of the anterior circulation in two patient and that of the border territory in one. The obstruction of large intracranial or extracranial vessels was detected in all of the patients, and all of them were treated with antiplatelet agents (aspirin or ticlopidine). The outcome was good in 3 patients, fair in one and bad in two. We retain that ET might be a cause of acute ischemic stroke as a result of large vessel obstruction.