378 duodenal polyps were identified by endoscopic biopsy since 1973 in the course of more than 25,000 oesophago-gastro-duodenoscopies, corresponding to an incidence rate of 1.5%. Heterotopias of the gastric mucosa and so-called inflammatory polyps were most frequent (35.7% and 35.2%, respectively), followed by hyperplasia of Brunner's glands (6.9%), lipid islets (2.9%) and lymphatic hyperplasia (1.8%). Histologically there was no correlate to the endoscopic findings. Hence, non-neoplastic polyps account for about 90% of duodenal polyps; they are harmless and generally produce no (or only minor) signs or symptoms. Clinically relevant polyps besides the primary and secondary malignant processes are the adenomas of the colon type (6.9%) and Peutz-Jeghers polyps (1.3%). Since these two may occur in gastrointestinal polyposis, "top-and-tail endoscopy" must be performed. The rate of complications of 15% in endoscopic loopectomy in the duodenum is clearly higher than that in the stomach and colon.