The possibility of an inflammatory lesion of the duodenal bulb is not considered frequently enough in the differential diagnosis of gastro-intestinal tract upsets or abdominal pain in children. For one to suspect ulcer in children presenting symptoms referable to the abdomen or gastro-intestinal tract, it is essential to accept the fact that ulcer can and does occur. The purpose of this paper is to cite some significant observations from the literature regarding duodenal ulcer and to present a series of illustrative case histories and roentgenograms of the lesion in children. Thiele (1) reported a series of 248 cases of ulcer in children sixteen years old or younger, half of which were duodenal in location. Hirsch (2), in a very large collected series of peptic ulcer, reported the incidence in children to be between 0.3 and 1.0 per cent, but did not distinguish between duodenal and gastric lesions. Cockovic (3) showed that more than 18 per cent of his cases of ulcer presented clinical symptoms developing between the ages of ten and twenty years. Proctor (4), in an analysis of 1,000 duodenal ulcers in adults, found 26 cases with symptoms dating back to childhood. Bird and his associates (5), in a careful search of the literature, discovered 119 cases of peptic ulcer in infants and children verified by operation, together with 124 cases in which the diagnosis was established by postmortem or x-ray studies. In this group of 243 cases, there were approximately 160 duodenal ulcers. Berglund (6) reported an analysis of 1,323 postmortem examinations in children up to thirteen years of age, in 14 of which duodenal ulcer was demonstrated. Benner (7) in 500 routine autopsies in children reported an incidence of duodenal ulcer of 1.4 per cent. Michaëlsson (8) reported an incidence of duodenal ulcer of 1.5 per cent. The true incidence of duodenal ulcer in children is difficult to evaluate. From scattered autopsy statistics, it would appear to vary from 1 to 1.5 per cent. This would seem to be a very significant percentage, for we know that autopsy statistics based on hospitalized patients do not represent the true incidence of a disease for any age group of the population, but only for that percentage with complications severe enough to require hospital admission. This would suggest that the true incidence of duodenal ulcer in children is much higher and that clinically it should be suspected more frequently and procedures instituted to prove or disprove its presence. This report is based on an x-ray study of the gastro-intestinal tract in 254 children in the routine work of an x-ray department in a general hospital and in private office practice. In this number of examinations, the x-ray diagnosis of duodenal ulcer was made 30 times. The oldest patient in whom ulcer was diagnosed was fourteen years of age, while the youngest was two years of age.