BACKGROUND Accurate preoperative staging of tumors of the esophagus and stomach is important in selecting treatment and determining prognosis. To date, no exact preoperative test has been useful in assessing stage of these tumors. Until recently, computed tomographic (CT) scanning has been the most frequently used examination to predict operative findings. Endoscopic ultrasonography (EUS) is a relatively new modality used by some centers to assess extramural anatomy of tumors in these two locations. METHODS We described 28 patients with tumors involving the esophagus and gastroesophageal junction, and the stomach, who underwent both EUS and CT before surgical exploration. We compared these two tests with the final pathologic interpretation and paid particular attention to presence of lymph nodes and wall penetration by primary tumor. RESULTS For wall penetration by an esophageal-gastroesophageal junction carcinoma, EUS was 85% accurate versus 15% for CT. For absence of nodal spread by these tumors, EUS was 100% accurate versus 67% for CT. In the presence of nodal spread EUS was 60% accurate versus 50% for CT. For wall penetration by a gastric carcinoma, EUS was 71% accurate versus 0% for CT. In the absence of nodal spread EUS and CT were both 100% accurate. In the presence of nodal spread EUS was 50% accurate versus 25% for CT. CONCLUSIONS EUS is more accurate than CT in the preoperative staging of upper gastrointestinal malignancies.