OBJECTIVE: The degree of carotid artery stenosis, as calculated by catheter-based angiography using NASCET methodology, has been shown to predict stroke risk in several large randomized controlled trials. In the current era, patients are increasingly being evaluated with CT-angiography (CTA) prior to carotid artery revascularization, especially as transcarotid artery revascularization (TCAR) adoption grows. Interpretation of CTA for degree of carotid stenosis has not been standardized, with both NASCET methodology and area stenosis being used. We performed a single-institution, blinded, retrospective analysis of CTAs using both NASCET methodology and CT-derived area stenosis to assess concordance/discordance between the two methods when evaluating > /=70% and > /=80% stenosis. METHODS: The UMass Memorial Medical Center vascular lab database was queried for all carotid duplex ultrasounds performed from 2008-2017. The dataset was winnowed to patients with duplex-defined > /=70% stenosis (defined as peak systolic velocity (PSV) > /=125 cm/s and an internal carotid-to-common carotid (ICA:CCA) ratio > /=4), and a correlative CTA performed < 1 year from duplex. A blinded review of all correlative CTA, using centerline measurements on a 3D workstation (Aquarius iNtuition Viewer, Terarecon, Durham, NC) was performed to characterize the degree of carotid stenosis by NASCET methodology and by area stenosis. Patients were excluded if revascularization was performed between the two imaging studies. RESULTS: Of 37,204 carotid duplex ultrasounds reviewed (2008-2017), 3,480 arteries met criteria for duplex defined > /=70% stenosis. A correlative CTA within 1 year of the duplex was identified in 460 arteries, of which 320 were adequate quality for blinded review. The median days between duplex and CTA was 9.5 days. Concordance between area and NASCET methodologies were poor for both > /=70% (kappa = 0.32) and > /=80% stenosis (kappa = 0.25). Of 247 arteries considered to have > /=70% area stenosis, 127 (51.4%) were considered to have > /=70% NASCET stenosis. Of 169 arteries considered to have > /=80% area stenosis, 44 (26.0%) were considered to have > /=80% NASCET stenosis. CONCLUSIONS: Area stenosis CTA calculations of carotid artery stenoses dramatically overestimate the degree of carotid stenosis compared to that calculated by NASCET methodology. Given that stroke risk estimates are based on trials that used NASCET methodology, area stenosis likely overestimates the risk of stroke. Therefore, area stenosis calculations may lead to unnecessary carotid revascularization procedures. This model highlights the need for standardized utilization of NASCET methodology when utilizing CTA as the imaging modality to determine threshold for carotid revascularization.