We compared the results of endoscopic sonography and CT in the preoperative staging of 46 patients with esophageal carcinoma studied prospectively. All patients had surgery and 44 had pathologic examination of the mediastinal and celiac lymph nodes. The results of CT and endoscopic sonography were compared with surgical and pathologic findings. A total of 51 tumors were found in 46 patients. Sonographic estimation of tumor extension through the different layers of the esophagus was correct in 37 (73%) of all 51 tumors and in 22 (85%) of the 26 tumors in which the examination was complete. The echoendoscope (13-mm diameter) could not pass through the tumor in 23 cases (50%). Infiltration to adjacent organs was found in 15 cases at surgery. In four of these 15, the extension was detected by CT; in seven of the 15 cases, it was detected by sonography. False-negative determination of tumor extension occurred with endoscopic sonography in patients with stenotic tumor. There were no false-positive results with either CT or endoscopic sonography. For detection of mediastinal lymph-node involvement, the sensitivity of CT was 48%. The sensitivity of sonography was 50% if metastatic nodes unexplored by sonography were included, or 84% if only cases in which stenosis was passed were considered. Statistical comparison revealed that sonography was superior to CT for the detection of metastases to lymph nodes. CT and endoscopic sonography provide complementary information. When the echoendoscope can be maneuvered past the tumor, sonography can be used accurately to define extension through the layers of the esophagus, extension to the adjacent organs, and involvement of the lymph nodes. When the tumor cannot be passed by the echoendoscope, CT is superior to sonography for detection of mediastinal extension.