The results of endosonography and computed tomography, using an optimized CT technique, have been compared in the preoperative detection of intrathoracic tumor spread of esophageal cancer. In 22/40 patients with esophageal tumors complete passage of the ultrasonic endoscope was possible. Endosonography was superior to CT in the assessment of early stage of esophageal tumor (T1-2). Out of 9 tumors confined to the esophageal wall, 8 were classified correctly by endosonography and only 5 by computed tomography. The results in advanced T3 and T4 tumors (13 patients) were comparable following endosonography and computed tomography. Endosonography is an important means of selecting patients with early-stage cancers in whom a curative resection is still a possibility.