['Controversy exists about whether occlusion of the contralateral internal carotid artery in patients undergoing carotid endarterectomy (CEA) is associated with a worse perioperative prognosis and outcome.', 'A systematic review of electronic information sources was undertaken to identify studies comparing perioperative and early outcomes of CEA in patients with occluded and patent contralateral carotid arteries. The methodologic quality of selected studies was independently appraised by two reviewers. Fixed- and random-effects models were applied to synthesize outcome data.', 'Our literature search located 46 articles eligible for inclusion in the review and analysis. The total population comprised 27,265 patients having undergone 28,846 CEAs (occluded contralateral artery group, 3120; patent contralateral artery group, 25,726). Patients with an occluded contralateral carotid artery had increased incidence of stroke (odds ratio [OR], 1.65, 95% confidence interval [CI], 1.30-2.09), transient ischemic attack (OR, 1.57, 95% CI, 1.11-2.21), stroke/transient ischemic attack (OR, 1.52; 95% CI, 1.21-1.90), and death (OR, 1.76; 95% CI, 1.19-2.59) ≤30 days of treatment compared with those with a patent contralateral vessel. No difference in the incidence of myocardial infarction between the two groups was identified (OR, 1.45; 95% CI, 0.73-2.89).'] Does contralateral occlusion of the internal carotid artery increase the risk of patients undergoing carotid endarterectomy?