Tapia's syndrome, first described in 1904 by A.G. Tapia, is considered to be a syndrome consisting of ipsilateral hemiplegia of larynx and tongue with spared movement of soft palate. A 61-year-old Japanese woman had been in good health until August 1991, when she developed hoarseness and atrophy of the left side of her tongue. Although she also showed mild disturbance of elevation of bilateral soft palates and loss of taste in the posterior third of her tongue as well, the main symptoms were the paralyses of the ipsilateral larynx and tongue without involvement of the ipsilateral sternocleidomastoid and trapezius muscles. We concluded that she had cranial polyneuropathy similar to that of Tapia's syndrome. A carotid angiography revealed that she has a large aneurysm, which originated from the extracranial internal carotid artery in the region near the skull base. No other abnormal findings were detected by any computed tomography, magnetic resonance imaging or 67Ga-scintigraphy. The patient's lower cranial polyneuropathy was considered to be caused by the aneurysm. A survey of the literature indicates that extracranial carotid aneurysm is an extremely rare cause of Tapia's syndrome. In this case, the location of the aneurysm, which was present considerably distant from the skull base, seems to be the reason for the sparing of the accessory nerve.