Forty-five polyps were encountered at duodenoscopy between 1973 and 1978. Upper gastrointestinal x-rays were helpful in 25 patients, 13 of whom had duodenal polyps and 12 duodenal deformity or mass lesions. Polyps in 23 patients were larger than 1 cm in size. Biopsies were done in 38 patients; in 19 there was only normal duodenal mucosa or chronic inflammation. Eight adenomatous polyps, six villous adenomas, two Brunner's gland hyperplasia, two lipomas, and one carcinoid tumor were found. Surgery was performed in eight patients and endoscopic polypectomy in four. We conclude that 1) small duodenal polyps are frequently missed on upper gastrointestinal x-rays, but these are submucosal polyps of little significance; 2) in general, polyps cannot be differentiated endoscopically into tissue categories, but villous adenomas show some characteristic features which allow a dependable endoscopic diagnosis; 3) a villous adenoma warrants excision because of the high incidence of malignancy; and 4) pedunculated duodenal polyps can be removed safely with endoscopic snare excision.