This is a study of 11 cases of duodenal tumors encountered in 1200 consecutive duodenoscopic examinations over a 34-month period at The Johns Hopkins Hospital. Of these tumors, 4 were benign and 7 malignant. Endoscopic removal of 2 benign tumors was accomplished without morbidity and obviated the necessity for transabdominal surgery. The 2 other benign tumors were a probable lipoma and a benign polyp, and did not require surgical intervention. In 6 of the 7 patients with malignant lesions, the indication for performing duodenoscopy was an abnormal roentgenographic study. In each case, direct visualization of the abnormal area, together with biopsy and cytologic brushing, provided a definitive diagnosis of malignant disease and helped plan the therapeutic course. In the seventh patient, a primary adenocarcinoma at the duodenojejunal junction was found on endoscopic examination, after all other available diagnostic studies to find the cause of persistent gastrointestinal bleeding had been exhausted. Although duodenal tumors are not common, they were encountered in 1 of every 100 duodenoscopies at a referral center. With increasing use of fiberoptic endoscopy, such tumors will undoubtedly be seen with increasing frequency. In our experience, endoscopy has proved to be a safe and reliable method of distinguishing between benign and malignant duodenal neoplasms and of assistance in planning subsequent management.