A 59-year-old man with no prior neurological deficits developed a massive stroke during the repair of a double-barreled acute type A aortic dissection with major entry in the ascending aorta and an occluded brachiocephalic artery. As right cerebral ischemia was alleviated by the circle of Willis, the patient was alert and conscious preoperatively. Nevertheless, the thrombus in the right carotid artery induced a severe postoperative right cerebral embolism. In conclusion, occlusion of the carotid artery is a risk factor of postoperative severe stroke, even in patients without neurological symptoms preoperatively.