Adenomatous polyps of the duodenum is uncommon in general population, but duodenal adenomas are found in the majority of patients with both familial adenomatous polypasis and Gardner's syndrome. These polyps are usually small, multiple and most commonly found in the second portion of the duodenum, and may involve ampulla of Vater. They also have malignant potential so that routine surveillance of the duodenum including ampulla of Vater has been recommended in patients with adenomatous polyposis coli. The adenoma of ampulla of Vater can be found in approximately 50% of patients with familial adenomatous polyposis and usually is asymptomatic, but sometimes, especially villous adenoma, may exhibit clinical problems including partial gastric outlet obstruction, pancreatitis, bleeding, obstructive jaundice, in addition to a high incidence of malignancy. Among the non-malignant complications of the ampullary tumor, there are only a few case reports of acute pancreatitis as the presenting manifestation of an ampullary adenoma or carcinoma in patients with familial adenomatous polyposis in the English literature, but no cases have been reported in Korea. We present here a case of symptomatic adenoma of the ampulla of Vater presenting as acute pancreatitis in a patient with familial adenomatous polyposis. (Korean J Gastrointest Endosc 17: 878-884, 1997)