Long-term evaluation of patients with aneurysms of the internal carotid artery (ICA) treated by intravascular balloon occlusion has not been reported. From 1977 to 1992, 58 patients (age 14 to 81 years) with ICA aneurysms were treated at our institution by this technique. The aneurysms included 40 intracavernous carotid, 5 petrous carotid, 3 cervical carotid, and 10 ophthalmic segment aneurysms. Presenting symptoms were caused by mass effect in 45 patients, transient ischemia or cerebral infarction as a result of emboli in 6, subarachnoid hemorrhage in 4, and epistaxis in 3. Preoperative temporary balloon occlusion of the ICA combined with cerebral blood flow monitoring and induced hypotension were used to determine tolerance for occlusion. Two patients not tolerating test occlusion required an extracranial-intracranial bypass procedure, and another patient underwent extracranial-intracranial bypass prior to test occlusion because of contralateral ICA stenosis. In 55 patients, aneurysms were excluded from the circulation by either occluding the proximal ICA or trapping the aneurysm neck. In three patients, the aneurysm was directly obliterated with intravascular balloons with preservation of the parent ICA. Three patients died during treatment, one from subarachnoid hemorrhage and two from cerebral infarction. Mean follow-up was 76 months (range, 6 months to 15 years). Six patients who developed transient ischemia caused by emboli responded to volume expansion and anticoagulation treatment. Two patients developed a delayed infarction, and one patient developed aneurysm enlargement that required surgical clipping and obliteration. (ABSTRACT TRUNCATED AT 250 WORDS)