Background: Atherosclerotic disease of the aortic arch has been found to he associated with the risk of ischemic stroke. We have shown that atherosclerotic plaques ≤4 mm in thickness in the ascending aorta and proximal arch detected by transesophageal echocardiography are a risk factor for ischemic stroke. The purpose of this study was to evaluate the impact, if any, of plaque morphology (ulceration, hypoechoic plaques or calcification) on the risk of subsequent vascular events. Methods and Results: We followed for a period of 2 to 4 years, a cohort of 334 patients 60 years or older who were consecutively admitted with brain infarction and who had transesophageal echocardiography. The risk of vascular events in patients with plaques in the aortic arch according to the presence of surface ulceration, calcifications, and sessile or mobile thrombus was estimated during a total of 788 person- years of follow-up. Hypoechoic plaques, calcifications, and ulceration were more frequently found in patients with plaques ≤4 mm as compared with those with plaques <4 min. The presence of ulceration did not increase the relative risk of vascular events in patients with plaque ≤4 mm (the relative risk was 4.3 [P<.001] in those with ulceration and 5.7 [P<.001]) in those without ulceration. The lack of calcification did increase the risk of vascular events in patients with plaque ≤4 min. The highest relative risk of events was found among the patients with noncalcified plaques (relative risk, 10.3; 95% confidence interval. 4.2 to 25.2; P<.001). The risk of events was systematically higher in patients without calcifications than in patients with calcifications regardless of what other morphological features were considered. Conclusions: In patients with brain infarction, the risk associated with aortic plaque thickness (≤4 mm) is markedly increased by the absence of plaque calcifications. These findings are important for the design of therapeutic trials in such patients.