The first report of a case of primary carcinoma of the duodenum is found among the writings of Georginis Hamberger1 as early as 1746. In 1761, the letters of Giovanni Morgagni2 brought to light the clinical pathologic report of the second instance, in which the condition was localized in the first portion of the duodenum. This case was said to have been encountered no later than 1733. Almost a century elapsed before additional instances were recorded. It is noteworthy that among the records and memoirs of Richard Bright3 no reference to this condition is found. Following Chomel's4 paper in 1852, and that of Caillet5 in 1876, many other reports appeared. Additional instances have continued to appear in the literature. The present report deals with four cases of primary carcinoma of the duodenum that were observed clinically and diagnosed by a careful study of the microscopic specimens. We have also made