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Background and Purpose: Intracranial atherosclerotic stenosis (ICAS) is a common cause of stroke especially in Asia, but little is known about its prevalence in ischemic stroke patients in North America. We studied the prevalence of ICAS in a single comprehensive stroke center leveraging the routine acquisition of MRI and MR angiography (MRA).Methods: We retrospectively reviewed patients with ischemic stroke and transient ischemic attack who were admitted within seven days of onset from Jan 2014 to July 2016. Patients we excluded: 1) Age <18 years; 2) without intracranial angiography; 3) overt cardiogenic occlusion or risk factors. Data were retrieved including demographics, vascular risk factors, brain imaging including MRA, CTA, and /or DSA, and prior medical prevention of stroke. ICAS was defined as the proximal atherosclerotic stenosis or occlusion ≥50% in diameter. We estimated the prevalence of ICAS at this single stroke center.Results: 685 included patients were aged 20 to 101 years, 384(56.1%) were men, 520 (75.9%) were white, and 74(10.8%) were black. ICAS was prevalent in 41.6% ofall included patients. Univariate analysis indicated that the prevalence of ICAS was significantly increased along with age, it was 39.3% for 41-60 years, and 43.8% for 61-80 years (P=0.034). But no significant difference was found between different races, it was 40.8% in Whites, and 40.5% in Blacks, and other races were 47.3%. Patients with ICAS had more severe stroke (NIHSS>3 vs NIHSS≤3: OR 2.729; 95%CI: 1.748-4.260; P<0.001). Higher levels of high-density lipoprotein cholesterol were associated with decreased odds of ICAS (OR 0.981; 95% CI: 0.968-0.995; P<0.006). Our data did not show hypertension, dyslipidemia and body mass index and smoking were associated with ICAS.Conclusions: The prevalence of ICAS in North America may be much higher than previous estimates. The impact of this common cause of recurrent stroke warrants further study, even in populations were cardiogenic embolic risk is common.