The use of endoscopic ultrasonography (EUS) for diagnosing the depth of carcinomatous invasion into the esophageal wall and in detecting mediastinal lymph nodes in patients with esophageal carcinoma was assessed. EUS was performed before surgery in 33 patients who underwent subtotal esophagectomy with lymph node dissection in our department of surgery between January 1987 and February 1989. The findings of EUS prospectively correlated with intraoperative macroscopic findings and histopathologic findings of the resected specimens. An accurate diagnosis of the depth of invasion into the esophageal wall was made in 30 of the 33 patients (90.1%). Visualization rates of mediastinal lymph nodes were 92.9%, 53.1%, and 1.0% when the nodes were greater than 10 mm in maximum diameter, 5 to 9 mm, and less than 5 mm, respectively. Although EUS had no diagnostic value for patients in whom the ultrasonic probe could not be inserted beyond the tumor, it is an excellent method for evaluating the depth of invasion and detecting lymph nodes greater than 10 mm in diameter. Detection is not feasible when the lymph node is less than 5 mm in diameter. EUS provides the surgeon with one more tool for the preoperative determination of curability.