A prospective study was carried out to examine the usefulness of endosonography (ES) in the pre-operative staging of patients with carcinoma of the esophagus, and its relevance in predicting resectability and the type of resection. The results of ES were compared with staging by conventional pre-operative methods and with operative staging according to the new American Joint Commission of Cancer staging classification. Of the 89 patients studied, 62 had a resection, 22 a bypass operation, and 5 had no operation. ES examination was unsuccessful in 19 patients because of complete or near complete tumor obliteration of the esophageal lumen and was incomplete in 13 patients because of distal tumor obstruction. These 32 patients accounted for 36% of all ES examinations, 27% of resection group, 55% of bypass group, and 60% of no operation group. The 45 patients who had a satisfactory ES examination and who had underwent a transthoracic resection were analyzed. The sensitivity and specificity of ES in detecting the depth of esophageal involvement were 89% and 96%, respectively, and for lymph node metastasis were 85% and 86%, respectively. However, ES was neither sensitive in detecting extra-esophageal infiltration to mediastinal organs nor was it able to determine the extent of intra-abdominal spread. The accuracy of pre-operative staging was 82% by ES compared with 51% by conventional staging (p < 0.001). ES correctly identified more advanced stage of disease in 14 (31%) patients as compared with conventional staging. On the evaluation of resectability, which was based on conventional investigations without ES, the result was unaffected even if the additional findings of ES were available.(ABSTRACT TRUNCATED AT 250 WORDS)