Septic necrosis of the internal carotid artery is a major complication of peritonsillar abscess. Although once a common complication, its occurrence is rare since the introduction of antibiotics. A 12-year-old girl was referred to our institution after a false aneurysm of the internal carotid artery had been entered during routine tonsillectomy for a peritonsillar abscess. Review of the literature and features of the present case demonstrate the following findings suggestive of erosion of the internal carotid artery as a result of peritonsillar abscess: (1) spontaneous hemorrhage from a peritonsillar abscess, (2) persistent peritonsillar swelling after resolution of symptoms of peritonsillar abscess, (3) ipsilateral Horner's syndrome, and (4) otherwise unexplained cranial nerve palsies (nerves IX, X, XI, and XII).