This study was conducted to perform a quantitative analysis and to identify predictors of embolic filter debris (EFD) load during carotid artery stenting (CAS) in asymptomatic patients. All patients with asymptomatic carotid stenosis ≥70% undergoing CAS between 2008 and 2016 were included in a prospective database. A distal filter protection was used in all patients. At the end of the procedure, the filter was fixed in formalin and then analyzed with a stereomicroscope. Morphometric analysis was performed with Image-Pro Plus software (Media Cybernetics). The total area of the filter membrane and the area covered by particulate material were quantified. The percentage of membrane occupied by debris was expressed as the percentage of covered surface area. Anatomic and clinical variables were evaluated for their association with EFD load using multiple logistic regression. Among the 278 patients undergoing CAS, an open-cell stent was implanted in 214 patients (78%), and 62 patients (22%) received a closed-cell stent. Overall technical and clinical success were both 99%. No perioperative death was reported. Stroke rate was 1% (major: n = 1 [0.4%]; minor: n = 2 [0.7%]), and transient ischemic attacks (TIA) occurred in 5.7% (n = 16). The quantitative analysis of the filters revealed that EFD was present in 74% (n = 207). The mean EFD load was 10% ± 14% of the filter surface (median, 1%; range, 0%-80%), and was ≤10% in 132 patients (47.5%), between 11% and 20% in 39 (14%), between 21% and 30% in 14 (4%), and ≥31% in 22 (8%). Patients with any type of ischemic neurologic event after CAS (stroke and TIA) had a significantly higher mean EFD load compared with uneventful cases (26.7% ± 19% vs 8.5% ± 13.5%; P < .001). The observational frequency distribution (Fig) identified the presence of >12.5% EFD load as the optimal cutoff for the association with clinically relevant perioperative ischemic events (sensitivity, 78%; specificity, 77%; area under the curve, 0.81). The multivariate analysis demonstrated that age >75 years (odds ratio [OR], 2.56; P = .003), pre-existing ipsilateral ischemic cerebra lesions (OR, 2.09; P = .04), hypoechogenic plaque at the preoperative duplex ultrasound study (OR, 6.05; P < .001), and plaque length >15 mm (OR, 1.79; P = .04) were independent predictors of EFD load >12.5%. Most patients with asymptomatic carotid stenosis treated with CAS have detectable embolic debris in the protecting filter. Age >75 years, pre-existing ipsilateral cerebral ischemic lesions, hypoechogenic plaque, and plaque length >15 mm, should be taken in consideration as independent predictors of clinically relevant embolic debris during the procedure.