['Selective shunting during carotid endarterectomy is widely performed, but the optimal approach for predicting when a shunt is unnecessary remains uncertain. We evaluated the ability of preoperative cerebral angiography to predict when carotid endarterectomy could be safely performed without a shunt.', 'Eighty-seven patients undergoing carotid endarterectomy between August 1991 and December 1997 had preoperative cerebral angiograms. The angiograms were evaluated for the presence of collateral flow from the contralateral carotid through the anterior communicating artery and from the posterior circulation through the posterior communicating artery. Patients then underwent endarterectomy and were selectively shunted based on somatosensory evoked potential changes. Internal carotid artery stump pressure was routinely measured in all patients.', 'Nine patients (10%) had a shunt placed based on somatosensory evoked potential changes and none of the 87 patients had a perioperative (30 days) stroke. Angiography revealed that 36 patients (41%) had no cross-filling from the contralateral carotid through the anterior communicating artery. Nine of these patients (25%) required a shunt; none of the 51 patients with adequate cross-filling (p < 0.001) did. Furthermore, 94% of the patients without cross-filling but with a patent ipsilateral posterior communicating artery did not require a shunt using somatosensory evoked potential changes as the standard for shunt insertion. Stump pressure measurements (> or = 25 mmHg) or (> or = 50 mmHg) did not reliably exclude the need for a shunt. Only 2 of 15 patients with contralateral carotid occlusion and 1 of 16 patients with a prior ipsilateral stroke required shunts.'] Do angiographic criteria reliably predict when carotid endarterectomy can be safely performed without a shunt?