Microembolization after carotid artery stenting (CAS) and carotid endarterectomy (CEA) has been documented and may confer risk for neurocognitive impairment. Patients undergoing stenting are known to be at higher risk for microemoblization. In this prospective cohort study, we compared the microembolization rates for patients undergoing CAS and CEA and patient and perioperative characteristics that may be associated with microembolization. Patients undergoing CAS and CEA were prospectively recruited under local institutional review board approval from an academic medical center. All patients also received 3T brain magnetic resonance imaging with a diffusion-weighted imaging sequence preoperatively and within 48 hours postoperatively to identify procedure-related new embolic lesions. Preoperative, postoperative, procedural factors, and plaque characteristics were collected. Factors were tested for statistical significance with logistic regression. There were 202 patients enrolled in the study; 107 underwent CAS and 95 underwent CEA. Patients undergoing CAS were more likely to have microemboli than patients undergoing CEA (78% vs 27%; P < .05). For patients undergoing CAS, patency of the external carotid artery (odds ratio, 11.4; 95% confidence interval, 1.11-117.6; P = .04), lesion calcification (odds ratio, 5.68; 95% confidence interval, 1.12-28.79; P = .04), and lesion length (odds ratio, 0.29; 95% confidence interval, 0.08-1.01; P = .05) were all found to be independent risk factors for postoperative embolization. These factors did not confer increased risk to patients undergoing CEA. Patients undergoing CAS are at higher risk for postoperative embolization. The risk for postoperative embolization is related to the length of the lesion and calcification. Identifying the preoperative risk factors may help to guide patient selection and, thereby, reduce embolization-related neurocognitive impairment. Understanding these risky lesions may also help to guide the selection of technique when selecting CAS or CEA for a patient and decrease morbidity. Patients undergoing stenting for atherosclerotic disease, therefore, may be at greater risk for embolization and neurocognitive impairment than those undergoing CAS for radiation-induced stenosis or other indications.