We report herein the case of a 56-year-old woman who presented with repeated transient ischemic attacks (TIAs). Cerebral angiography revealed that the left redundant internal carotid artery (ICA) uncharacteristically curved medially. These findings were highly suggestive of an internal carotid artery aneurysm at the level between the first and second cervical vertebral bodies. The lesion was presumed to be difficult to access by the surgical procedure usually adopted in carotid endarterectomy. Thus, we decided to employ a modified vertical mandibular osteotomy. The operative view revealed that the lesion was atherosclerotic stenosis with ulceration, so carotid endarterectomy was indicated. This mandibular osteotomy not only provided us with wide, satisfactory exposure of the distal cervical internal carotid artery but also afforded good mandibular stability during the postoperative period.