To asses the diagnostic accuracy of endoscopic ultrasonography (EUS) for the local and regional staging of esophageal cancer, and its possible alteration resulting from the performance of preoperative chemoradiation.Prospective study of 85 consecutive patients with esophageal cancer evaluated by EUS and operated between January 1992 and December 1995. 28 of these patients had received previous induction therapy. In all cases, EUS examination was performed by the same physician not informed about the results of previous morphological explorations. Histopathological analysis of all specimens was performed by the same pathologist, not informed about the results of the EUS. Data were collected by another independent observer.EUS examination resulted in incomplete staging in 8 patients (9.5%) with severe stenosis precluding endoscope passage. The accuracy, specificity and sensibility of EUS in detecting the depth of esophageal involvement (T0-2 vs T3-4) were 82.3%, 78% and 86% respectively, and 72%, 70% and 73% respectively for the lymph node metastasis. The overall accuracy of EUS in identifying the preoperative stage was 67% with a clear-cut alteration when patients had received induction therapy (61% vs 72%). On the other hand, 7(64%) of the 11 patients thought to have a complete response at endosonography had no residual tumor.EUS provides precise information for the preoperative identification of locally advanced esophageal tumor, even after induction therapy. The latter alters the diagnostic accuracy of EUS, although complete responders could be identified in two-thirds os cases.