To assess the extent of mediastinal spread, especially to the left main bronchus and the descending aorta, CT findings were analyzed in 42 patients with mid-thoracic (Im) esophageal carcinoma. The minimum distance between the anterior margin of the vertebral body and the left main bronchus, the minimum inner diameter of the left main bronchus and the maximum size of the tumor were measured and used as diagnostic criteria. CT was capable of evaluating the invasion to the left main bronchus when the minimum distance between the anterior margin of the vertebral body and the left main bronchus was more than 21 mm and the minimum inner diameter of the left main bronchus was less than 8 mm, and to the descending aorta when the tumor was more than 31 mm. CT accurately outlines the extent of lesions and is helpful in determining the type of surgical procedure and in planning radiation therapy.