The authors report 9 patients who presented with loss of consciousness (syncope) due to occlusive carotid artery diseases. All patients were males, and their age ranged from 59 to 83 years. The attack was associated with dehydration or hypotension in 5 patients. MRI demonstrated fresh cerebral infarction in the watershed zone. Cerebral angiography revealed occlusion of the unilateral internal carotid artery (ICA) in 7 patients, severe stenosis of the bilateral ICA in one, and occlusion of the unilateral ICA and severe stenosis of the contralateral ICA in one. Single photon emission tomography (SPECT) or positron emission tomography (PET) suggested reduced cerebral perfusion reserve because of inappropriate development of collateral circulation in 4 out of 9 patients. These 4 patients underwent superficial temporal artery to middle cerebral artery anastomosis and/or carotid endarterectomy. Other 5 patients were medically treated. No further episode of syncope occurred in all 9 patients during follow-up periods. The results suggest that occlusive carotid artery diseases should be taken in considerations as a cause of syncope attack.