['Brain white-matter lesions and cognitive impairment are increasing because of the increasing number of patients aged ≥80 y. Wall shear stress (WSS) plays a pivotal role as a fluid mechanical mediator in vascular reactivity and atherosclerosis. In this study, we investigated the associations among common carotid artery (CCA) WSS, white-matter lesions, and cognitive impairment in patients aged ≥80 y', 'We enrolled 384 patients aged ≥80 y. All subjects had CCA-WSS, brain white-matter hyperintensities (WMH), and Mini-Mental State Examination (MMSE) assessments and were divided into three groups using tertiles of mean and peak CCA-WSS.', 'For groups classified by the tertile of mean CCA-WSS, WMH, and WMH fraction were decreased; the MMSE score increased from low to high in the respective groups. Differences in WMH, WMH fraction, and the MMSE score were significant between any two groups (all adjusted p < 0.001). Groups classified by the tertile of peak CCA-WSS had the same pattern. Mean and peak CCA-WSS were significantly and inversely correlated with WMH (r = -0.575 and -0.570, respectively; p < 0.001) and WMH fraction (r = -0.574 and -0.569, respectively; p < 0.001) but positively correlated with the MMSE score (r = 0.390 and 0.278, respectively; p < 0.001). Multiple linear backward stepwise regression indicated the mean and peak CCA-WSS were significantly and independently associated with WMH, WMH fraction, and the MMSE score (all adjusted p < 0.001).'] Is low carotid artery wall shear stress independently associated with brain white-matter hyperintensities and cognitive impairment in older patients?