Eagle syndrome is a rare condition induced by an elongated styloid process. A 51-year-old man became aware of weakness and numbness of the right upper extremity. Magnetic resonance images and angiography revealed fresh multiple infarctions in the left cerebrum, and stenosis and dilatation of the left internal carotid artery. Angiography, cone-beam computed tomography, and contrast-enhanced computed tomography demonstrated dissection of the left internal carotid artery and an elongated styloid process close to the internal carotid artery. These findings indicated that cerebral infarction due to internal carotid artery dissection resulted from mechanical compression by an elongated styloid process. The patient was treated by carotid artery stenting on the 7th day. His symptoms induced by cerebral infarction gradually improved. Follow-up MRI on the 29th day showed patency of the left internal carotid artery. Although the incidence of internal carotid artery dissection due to Eagle syndrome is low, the possibility of this rare condition should be taken into consideration as an etiology of cerebral infarction.