Transesophageal echocardiography (TEE) was performed in 17 cases of aortic aneurysms referred to our hospital for further examination and treatment. All 17 cases were treated surgically and TEE was performed as a preoperative examination. In nine of the 17 cases, there were already some signs of bleeding upon admission and in all of these nine cases, rupture of the aneurysm was confirmed during surgery. Measurement on cross-sectional TEE imaging disclosed large aneurysmal diameters in eight of these nine cases, suggesting a close relationship between diameter and rupture. Moreover, observation of the lesions by TEE suggested a relationship between the risk of rupture and morphological characteristics of the thrombus. In seven of the nine bleeding cases, TEE imaging revealed destructive features of the aneurysmal thrombus, such as exfoliation from the aortic wall and/or tearing-off, suggesting expansion of the aortic diameter. Detailed findings of the aneurysm and thrombus on TEE corresponded with surgical findings. Thus, we concluded that TEE is a useful method of obtaining information about aortic aneurysms not only as a preoperative examination but also as an independent examination to determine treatment options and prognosis.