Eighty-eight patients with carcinoma of the esophagus (N = 44), stomach (N = 41), and duodenum (N = 3) who underwent surgery were pre-operatively examined by endoscopic ultrasonography (EUS). The ability of EUS to accurately predict the T stage and the N stage was 82% and 70% for esophageal carcinoma, 71% and 75% for gastric cancer, and 100% and 66% for duodenal malignancy. In esophageal carcinoma, the accuracy of T staging was only slightly lower in cases with non-traversable tumor stenoses (77%) compared with traversable carcinomas (84%). This was probably due to the fact that all non-traversable tumors were either in stage T3 or T4. The accuracy of EUS in predicting the stages T1 to T3, which correspond to R0 resectability (no macroscopic or microscopic tumor remains), was 92% for adenocarcinoma of the distal esophagus and 85% for gastric cancer. However, in squamous cell carcinoma of the esophagus, R0 resection was possible in only 66% of all cases, whereas EUS predicted an 84% R0 resection rate. In adenocarcinoma of the distal esophagus and stomach, EUS prediction of stages T1 to T3 correlated well with the actual rate of R0 resection. These results show that EUS is a reliable diagnostic method for the local staging of upper gastrointestinal cancer. Its impact on treatment and hence on prognosis of patients with these malignancies has yet to be determined.