Endoscopic ultrasound (EUS) of the esophagus has been used primarily in staging biopsy-proven cancers. Its use as a primary diagnostic modality for esophageal malignancy has not been previously described. We report our recent experience in four patients with dysphagia and endoscopic biopsies negative for malignancy, including one patient with clinical and manometric features suggestive of achalasia. In all cases, EUS revealed a large infiltrating tumor invading through the esophageal wall into the surrounding tissues, and in one case into the aorta. Computed tomography suggested the possibility of a tumor in only one of the cases. Two patients underwent esophagectomy and were found to have adenocarcinoma. Two patients underwent repeat biopsy with alternative aggressive biopsy techniques and were found to have squamous cell carcinoma. We conclude that EUS is useful in the diagnosis of esophageal cancer and should be performed in selected patients with esophageal strictures whose biopsies are negative for malignancy; i.e., those with suspicious endoscopic or radiographic appearance, atypical presentation (e.g., profound weight loss, short duration of symptoms, or advanced age), and failure to respond to treatment.