Background and Purpose— The significance of non-ST–elevation myocardial infarction (NSTEMI) after carotid endarterectomy or carotid angioplasty and stent placement is unknown. We performed this study to identify the frequency of NSTEMI and impact on outcomes related to carotid endarterectomy or carotid artery stent placement in patients treated in a large national cohort. Methods— We determined the frequency of NSTEMI and associated in-hospital outcomes including mortality and composite of stroke, cardiac events, and mortality using data from the Nationwide Inpatient Survey from 2002 to 2009. Results— Of 1 083 688 patients who underwent carotid endarterectomy or carotid artery stent placement, 11 341 (1%) patients developed NSTEMI during hospitalization. After adjusting for constitutional variables and risk factors, NSTEMI was associated with higher rates of in-hospital mortality (odds ratio, 8.6; 95% confidence interval, 7.0–10.7; P ≤0.0001) and composite end point of stroke, cardiac events, and death (odds ratio, 14.6; 95% confidence interval, 13.0–16.5; P ≤0.0001). Conclusions— Our results contradict the notion that NSTEMI is a relatively benign entity after carotid endarterectomy or carotid artery stent placement.