To assess the predictive value of carotid bruit for moderate-to-severe carotid atherosclerosis, the results of carotid arteriograms performed on 1004 subjects were correlated with the findings of auscultation of the carotid arteries. Predictive values of carotid bruit for ipsilateral extracranial carotid atherosclerosis were 77% for localized bruits and 74% for diffuse bruits. The predictive values of extracranial carotid bruit for ipsilateral intracranial carotid atherosclerosis were 16% for localized bruits and 18% for diffuse bruits. Assessing both carotid arteries together, the predictive value of carotid bruit for moderate-to-severe atherosclerosis at any extracranial carotid site was 85%, there being no difference whether the bruits were diffuse, localized, bilateral, or unilateral. Diffuse or localized bruits, whether unilateral or bilateral, are equally predictive of moderate-to-severe atherosclerosis in the extracranial carotid artery, but both are poor predictors of intracranial carotid artery disease.