This study was designed to evaluate the effectiveness of intra-aortic ultrasonography in the preoperative diagnosis of aortic wall invasion by oesophageal cancer. Twenty-four patients with advanced oesophageal cancer underwent the procedure, and aortic invasion was found in seven. In three of these seven patients, the invasion was diagnosed to be limited to the aortic adventitia, enabling preoperative prediction of the resectability of the tumour. The contact angle of the tumour in relation to the descending aorta was more than 90 degrees in six patients, and aortic invasion to all layers was visualized in four by intra-aortic ultrasonography. On the other hand, aortic invasion to the adventitia was found in three of 14 patients in whom the contact angle was less than 90 degrees. Intra-aortic ultrasonography provides important information to help determine the resectability of advanced oesophageal cancer.