We describe here successful surgical treatment of a rare case of a rapidly enlarged aneurysm due to Takayasu's arteritis. A 22-year-old woman presented with a 1-month history of hoarseness and left neck pain. Contrast-enhanced computerized tomography showed an unruptured partially thrombosed aneurysm, and angiography revealed a large aneurysm of the common carotid artery. After hospitalization, the symptoms, interestingly, resolved spontaneously. While angiography at 2 weeks after admission showed the aneurysm to have reduced in size, 2 months later it showed the left common carotid artery aneurysm to be substantially enlarged in size and aneurysmal formation of the right external carotid artery. Surgical intervention was performed for the left common carotid artery aneurysm because rapid enlargement indicated the risk of aneurysmal rupture, and the thrombosis might cause embolic occlusion of the cerebral arteries. The left common carotid artery including enlarged aneurysm was trapped and anastomosed with a Gore-Tex graft (6-mm inner diameter) to left internal carotid artery. Histological examination of the arterial wall showed inflammatory change, destruction of the medial elastic fibers, and granulation with multinucleated giant cells. The postoperative course was uneventful, and no new vascular lesion was observed 3 years after operation. We demonstrated the bilateral extracranial carotid artery aneurysms caused by Takayasu's arteritis, which was the first case to be reported in the literature.