Case reports of primary carcinoma of the duodenum, a rare and interesting condition, have appeared occasionally in the literature. The contributions of Crohn,1Eusterman, Berkman and Swan,2Meyer and Rosenberg,3Cohen and Colp,4Halsted,5Mayo,6Judd,7Ewing,8Rolleston9and Jefferson10are of especial interest. In several of the articles the literature has been tabulated comprehensively. However, the diagnostic criteria, differential diagnosis and associated pathologic findings of carcinomas arising from the three areas of the duodenum have not been generally appreciated. In view of this fact and because of the rarity of these cases, it seems worth while to report and analyze the following six cases, which illustrate lesions of each type. These six proved cases have occurred in 176,000 admissions to this clinic. Several representative statistical reports indicate that duodenal carcinoma constitutes about 0.25 per cent of all carcinomas, and