Primary adenocarcinoma of the esophagus is thought to be a rare lesion. However, pathologic records at our institution from 1979 to 1982 show that adenocarcinoma accounted for 17 of 89 (19%) of all primary malignant tumors in the esophagus. All 17 cases arose in Barrett mucosa. In eight cases, there was surgically proved involvement of the gastric cardia or fundus. In six of these cases, there was evidence of esophageal dysplasia and/or carcinoma in situ adjacent to or remote from the proximal margin of the tumor. The pathologic findings therefore strongly suggest an esophageal origin of these lesions with subsequent spread into the stomach. Clinical and radiographic findings at presentation were indistinguishable from those of squamous cell carcinoma. However, 10 patients had long-standing reflux symptoms, and Barrett esophagus had presumably been present for some time prior to the development of malignancy. Since adenocarcinoma evolves through a sequence of dysplasia and carcinoma in situ in pre-existing Barrett epithelium, the best hope for improving survival may be periodic endoscopic surveillance of asymptomatic individuals who have this condition.