Purpose: Aortic arch disease is an important embolic source of ischemic stoke. To evaluate aortic arch disease, CT angiography (CTA) and transesophageal echocardiography (TEE) have been regularly examined. Recently, thin slice CTA is used for evaluating coronary artery disease. Thus, we considered that thin slice CTA was also useful for detecting aortic arch disease. The aim of this study was to assess the usefulness of thin slice CTA in the evaluation of the aortic arch disease and to compare with that of TEE. Methods: We retrospectively enrolled acute ischemic stroke patients admitted to our hospital within 7 days of onset, from October 2016 to June 2018. The findings detected by thin slice (0.5-1.0mm) CTA were evaluated by two stroke specialized neurologists. The presence and localization of plaques and ulcers were evaluated. These findings were compared to those of TEE in case of which both examinations were underwent. Results: We enrolled 60 acute ischemic stroke patients (37 men, mean age 70 years) who underwent CTA. Large artery atherosclerosis was detected in 17 patients (28%), and atrial fibrillation was found in 6 patients (10%). CTA was mostly examined for searching embolic sources. Plaques of 4mm or more and ulcers were found in 29 (48%) and 22 patients (37%). Accordingly, 14 patients (23%) were diagnosed as aortagenic stroke. Among 29 patients with both examinations, plaques were detected in 22 patients (76%) by CTA and in 16 patients (55%) by TEE. The sensitivity and negative predictive value of TEE in detecting plaques compared with CTA was 73% and 100%. Plaques missed by TEE were mostly located on the side close to esophagus. Ulcers were highly investigated by CTA than by TEE (45% v.s. 17%, p<0.05). The sensitivity and negative predictive value of TEE in detecting ulcers compared with CTA was 31% and 94%. Conclusion: In this study, thin slice CTA was superior to TEE for detecting plaques located on the side close to esophagus and ulcers. Thin slice CTA may be useful for detecting embolic sources in ischemic stroke patients. <!--EndFragment-->