Forty-nine cases of surgically resected adenocarcinomas of the gastric cardia and 23 cases of resected adenocarcinomas arising in Barrett's columnar lined lower esophagus were compared histologically and clinically. Morphologically, the two groups were almost identical in terms of pattern of growth (expansile or infiltrative), degree of differentiation, and extent of spread at the time of operation. These similarities are not surprising, as the two carcinomas arise close to each other from almost identical mucosas. The major histologic difference was the finding of much more frequent dysplasia in the adjacent Barrett's mucosa than in the surrounding cardiac mucosa, probably a reflection of the larger surface area covered by Barrett's than by cardiac mucosa. The groups differed in certain epidemiologic parameters that possibly reflected independent carcinogenetic mechanisms. Thus, although the age ranges and median ages were the same, there was a higher male predisposition among the patients with cardiac carcinoma. In addition, patients with cardiac carcinoma had a significantly higher history of heavy smoking and history of alcohol intake, whereas those with Barrett's carcinoma were much more likely to have hiatal hernias.