OBJECTIVE: The Centers for Medicare and Medicaid Services (CMS) require high-risk (HR) criteria for carotid artery stenting (CAS) reimbursement. The impact of these criteria on outcomes after carotid endarterectomy (CEA) and CAS remains uncertain. Additionally, if these HR criteria are associated with more adverse events after CAS, then existing comparative effectiveness analysis of CEA vs CAS may be biased. We sought to elucidate this using data from the SVS Vascular Registry. METHODS: We analyzed 10,107 patients undergoing CEA (6370) and CAS (3737), stratified by CMS HR criteria. The primary endpoint was composite death, stroke, and myocardial infarction (MI) (major adverse cardiovascular event [MACE]) at 30 days. We compared baseline characteristics and outcomes using univariate and multivariable analyses. RESULTS: CAS patients were more likely to have preoperative stroke (26% vs 21%) or transient ischemic attack (23% vs 19%) than CEA. Although age ≥ 80 years was similar, CAS patients were more likely to have all other HR criteria. For CEA, HR patients had higher MACEs than normal risk in both symptomatic (7.3% vs 4.6%; P < .01) and asymptomatic patients (5% vs 2.2%; P < .0001). For CAS, HR status was not associated with a significant increase in MACE for symptomatic (9.1% vs 6.2%; P = .24) or asymptomatic patients (5.4% vs 4.2%; P = .61). All CAS patients had MACE rates similar to HR CEA. After multivariable risk adjustment, CAS had higher rates than CEA for MACE (odds ratio [OR], 1.2; 95% confidence interval [CI], 1.0-1.5), death (OR, 1.5; 95% CI, 1.0-2.2), and stroke (OR, 1.3; 95% CI,1.0-1.7), whereas there was no difference in MI (OR, 0.8; 95% CI, 0.6-1.3). Among CEA patients, age ≥ 80 (OR, 1.4; 95% CI, 1.02-1.8), congestive heart failure (OR, 1.7; 95% CI, 1.03-2.8), EF <30% (OR, 3.5; 95% CI, 1.6-7.7), angina (OR, 3.9; 95% CI, 1.6-9.9), contralateral occlusion (OR, 3.2; 95% CI, 2.1-4.7), and high anatomic lesion (OR, 2.7; 95% CI, 1.33-5.6) predicted MACE. Among CAS patients, recent MI (OR, 3.2; 95% CI, 1.5-7.0) was predictive, and radiation (OR, 0.6; 95% CI, 0.4-0.8) and restenosis (OR, 0.5; 95% CI, 0.3-0.96) were protective for MACE. CONCLUSIONS: Although CMS HR criteria can successfully discriminate a group of patients at HR for adverse events after CEA, certain CMS HR criteria are more important than others. However, CEA appears safer for the majority of patients with carotid disease. Among patients undergoing CAS, non-HR status may be limited to restenosis and radiation.