Background and Purpose-Recent randomized trials showed an increased periprocedural risk for stroke with increasing age in patients undergoing carotid artery stenting. Manipulation of atherosclerotic plaques during carotid artery stenting can result in plaque rupture with subsequent superimposed thrombus formation, embolization, and cerebrovascular events. We hypothesized that atherosclerotic plaques become more unstable with increasing age and thereby might provide insight into the age-related increased risk of cerebrovascular events during carotid artery stenting. Methods-Carotid atherosclerotic plaques were harvested from 1385 consecutive patients undergoing carotid endarterectomy between 2002 and 2010. Carotid plaques were quantitatively analyzed for macrophages, smooth muscle cells, and microvessels; and semiquantitatively analyzed for collagen, calcifications lipid cores, and intraplaque hemorrhages.Patients were divided in 4 groups by age: Ͻ60, 60 to 69, 70 to 79, and Ն80 years. Measures of association between age as a continuous variable and histological characteristics were also calculated. Results-Increasing age was associated with a decrease in the amount of smooth muscle cells in the carotid plaque. More plaques with large atheroma and heavy plaque calcifications were observed among elderly patients. After correction for baseline differences, risk factors, and medication use, age was independently associated with a more vulnerable carotid plaque composition. Conclusion-Plaque stability decreases gradually with age. Older patients with carotid stenosis have relatively unstable plaques with low smooth muscle cell content, a high amount of large lipid cores, and more calcified plaques as compared with younger patients. The underlying vulnerable plaque composition in the elderly might be an important contributing factor to the increased risk of stroke for older patients undergoing carotid artery stenting. (Stroke. 2011;42:2550-2555.)Key Words: age Ⅲ angioplasty & stenting Ⅲ atherosclerosis Ⅲ carotid stenosis Ⅲ plaque composition Ⅲ risk factors C arotid endarterectomy (CEA) reduces the risk of ischemic stroke in patients with a recently symptomatic, significant carotid artery stenosis. 1 Subgroup analysis revealed a high benefit from surgery, particularly for patients Ͼ75 years, due to the relatively high risk for a secondary event and therefore a relatively low number needed to treat to prevent 1 ipsilateral stroke. 2 Besides the favorable number needed to treat, overall life expectancy is rising, indicating that CEA in the "intellectually intact" elderly can be highly beneficial. 3 From observational studies, the periprocedural risk for the elderly undergoing CEA has been reported to be comparable to the risk for younger patients. 3-5 Nevertheless, subgroup analyses for age in several randomized trials revealed that periprocedural risk of stroke, myocardial infarction, and death after carotid artery stenting (CAS) increases with age. 6 -9 The occurrence of periprocedural stroke for CAS has been propos...