Two-dimensional transesophageal echocardiography (2D-TEE) facilitates clear imaging of the thoracic aorta, and we have already reported the diagnostic value of this procedure for detecting dissecting aortic aneurysm (DAA). Recently, we performed preoperative and postoperative 2D-TEE in nine surgically treated patients with DAA (Debakey type I: 2 cases, type II: 1 case, type IIIa: 2 cases, type IIIb: 4 cases), and repeated 2D-TEE in six medically treated patients (DeBakey type IIIa: 2 cases, type IIIb: 4 cases), and the usefulness of 2D-TEE in the follow-up study of DAA was evaluated. Two types of ultrasound probe (radial scan type, and sector type with a color-Doppler system) were used in this study. Of the surgically treated patients, four of nine cases in which the initial tears were excised or repaired showed neither leakage nor pseudoaneurysm at the site of graft insertion. Other surgically treated patients showed residual intimal tears and continued to harbor patent false lumen. One patient with type I dissection demonstrated localized saccular aneurysm in the proximal arch of the aorta, but no evidence of aortic regurgitation. Of the six medically treated patients, further extension of the initial dissection was observed in one of the two type IIIa cases. False lumen narrowing was recognizable in three of the four type IIIb patients, and complete obliteration of false lumen was observed at necropsy in one of these three cases. Double-channeled aorta was seen in another case of type IIIb dissection.(ABSTRACT TRUNCATED AT 250 WORDS)