Polycythemia vera (PV) can produce cerebral infarction. The mechanisms proposed by most authors are hyperviscosity-related diminished cerebral blood flow and platelet function abnormalities. We present a 36-year-old woman whose initial clinical manifestation of PV consisted of cerebral ischemia due to a carotid thrombus, as well as occlusion of the middle cerebral artery and cortical branches of the anterior cerebral artery demonstrated by angiography. To our knowledge, this is the first published case of cerebral infarction in PV caused by a thrombus of an extracranial artery. Therefore, PV can produce ischemic stroke due to thrombosis not only in small distal arteries or arterioles but also in the carotid artery or main branches. Treatment of intraluminal thrombus in non-arteriosclerotic carotid artery is discussed. Myeloproliferative disorders, including PV, must be suspected in all stroke patients with an elevated platelet count, even in those who have potential causes of reactive thrombocytosis.