Adenocarcinoma of the esophagus has been considered an uncommon tumor, accounting for fewer than 8% of all cases of esophageal cancer. To determine the current frequency of adenocarcinoma of the esophagus, we reviewed data from the tumor registries of the Commonwealth of Massachusetts, the University Hospital (UH), and the Boston VA Medical Center (BVAMC). From 1982 to 1984, 868 esophageal cancers were reported in Massachusetts, of which 231 (27%) were adenocarcinomas. In comparison with squamous cell carcinomas of the esophagus, esophageal adenocarcinomas occurred more frequently in males (P less than 0.01) and were uncommon among blacks (P less than 0.01). From 1980 to 1986, 262 cases of esophageal cancer were seen at the UH and the BVAMC, of which 81 (31%) were adenocarcinomas. An analysis of the latter group to identify true esophageal adenocarcinomas (tumors confined to the esophagus without gastric involvement) yielded 47 cases. Thus, true esophageal adenocarcinoma accounted for 18% of esophageal malignancies at our hospitals, a frequency threefold to fivefold higher than that found in four prior studies that used comparable anatomic diagnostic criteria. We conclude that adenocarcinoma of the esophagus is now being recognized at a substantially higher frequency than reported in the past.