Real-time color flow mapping by two-dimensional Doppler has now come into widespread use. However, its application via conventional transcutaneous approaches to dissecting aortic aneurysm has some limitations where visualization of the descending aorta is concerned. Its transesophageal approach to this disorder has hitherto remained unreported except by the authors. Transesophageal Doppler color flow mapping has been performed in twelve patients for diagnosis of dissecting aortic aneurysm, and the clinical significance of this method was evaluated. The system used for transesophageal color flow mapping was an Aloka SSD-880 ultrasound scanner with a 5 MHz probe. In all cases, the entire thoracic aorta except for the upper ascending aorta was visualized and both, real-time flow dynamics and structural information, were ascertained. Differentiation of the type of dissection, identification of the entry, and differentiation of the true and false lumina were performed in all cases. Information concerning the reentry was gained in seven cases (58%); aortic regurgitation was graded in three cases, in two of which prolapse of the intimal flap was observed. In five cases, aortography was needed in order to delineate the involvement of aortic branches in the dissection; and in the other seven cases, transesophageal Doppler information was sufficient. In four cases who were operated, the postoperative state was well evaluated. Transesophageal Doppler color flow mapping was found to be a useful method for visualization of the whole thoracic aorta apart from the upper ascending section, and for precise evaluation of the structure and hemodynamics of dissecting aortic aneurysms.