Transesophageal echocardiography (TEE) provides excellent images of the thoracic aorta, which cannot be visualized by transthoracic echocardiography. The purpose of this study was to assess atherosis and sclerosis of the thoracic aorta by TEE, to evaluate the risk factors for atherosis and sclerosis, and to assess the relationship between the two components of atherosclerosis. The mean value of the maximum thickness of the intima-media complex in the six segments of the thoracic aorta (MIMC) was used as an index of atherosis, and the stiffness parameter beta was used as an index of sclerosis. The study population consisted of 88 Japanese patients. Multivariate analysis showed that age, low-density lipoprotein cholesterol (or apolipoprotein B), and diabetes mellitus were significantly and independently related to MIMC, whereas age and hypertension were related to the stiffness parameter beta. Both components of atherosclerosis demonstrated a significant although weak relationship. The risk factors for atherosis appear to differ from those for sclerosis in the thoracic aorta, so we should evaluate these two components of atherosclerosis separately. TEE is a useful method of assessing thoracic aortic atherosclerosis because both atherosis and sclerosis can be examined simultaneously.