We report a 31-year-old woman with an intracavernous carotid aneurysm who experienced a cerebral embolic complication during the gradual occlusion of an internal carotid artery (ICA) following superficial temporal to middle cerebral artery anastomosis. The cerebral angiogram revealed an em bolus lodged in the stem of the middle cerebral artery. Based on our findings we suggest that in the presence of a sufficient collateral blood supply after extra and intracranial bypass surgery, abrupt ICA ligation may reduce the risk for thrombo-embolic complications. If, on the other hand, the col lateral blood flow is insufficient, gradual ICA occlusion should be considered and anticoagulant therapy should be used.