Endosonography, which provides high-resolution images of the esophageal wall, could potentially detect carcinoma not visible endoscopically in patients with Barrett's esophagus and high-grade dysplasia. We studied the ability of endosonography to detect early esophageal carcinoma in 9 patients with Barrett's esophagus and high-grade dysplasia who were candidates for esophagectomy. Pre-operative endoscopy and biopsy revealed high-grade dysplasia without evidence of carcinoma in all patients. Pre-operative endosonographic evaluations were compared to the pathologic diagnoses of resected specimens. Post-operatively, 3 of the 9 patients were found to have intra-mucosal carcinoma. Endosonography identified a tumor in only 1 of these 3 patients and over-staged it as invasive carcinoma (T2, N1). In 2 of the 6 patients without intra-mucosal carcinoma, endosonography predicted invasive carcinoma (T2, N0). Endoscopy revealed mucosal nodularity in each of the 3 over-staged patients. We conclude that recommendation of the routine use of endosonography to determine the need for surgery in patients with Barrett's esophagus and high-grade dysplasia would be premature, because the current generation of echo-endoscopes does not reliably differentiate between benign and malignant wall thickening.