Abstract Eleven new cases of Crohn's disease involving the duodenum are reported. It is rare for the duodenum to be involved without other segments of the bowel also being involved. Only one of our patients had isolated duodenal disease. The clinical presentation suggests peptic ulceration. Therapy is conservative, with surgery restricted to those patients with obstruction. The procedure of choice is bypass gastrojejunostomy. Six patients are now asymptomatic, four have had symptomatic relief, and one has died. It is likely that the incidence of Crohn's disease of the duodenum is more frequent than the number of reported cases would suggest, but that these cases are not diagnosed because of unfamiliarity with the condition.