Since Hamberger1 reported the first case of carcinoma of the duodenum in 1746, an extensive literature has accumulated, out of all proportion to the number of cases which have occurred. Little has been written, however, on the roentgenographic picture of the disease. This paper presents the results of a clinical and roentgenographic study of 18 cases of primary carcinoma of the duodenum, in 5 of which the patient was personally examined and studied during life by us. The data on these cases have been collected from seven different hospitals and have not been previously reported. INCIDENCE The rarity of primary cancer of the duodenum is shown by the following figures compiled from the statistics of various authors. The incidence of primary carcinoma of the duodenum in 350,286 autopsies was 0.033 per cent. Perry2 in 17,652 autopsies performed at Guy's Hospital found 6 primary sarcomas of the duodenum, from