Adenoma of the major papilla carries a relatively high risk of malignant transformation to carcinoma, the leading cause of death in patients with familiar adenomatous polyposis (FAP) after colectomy. A 35-year-old man had undergone prophylactic colectomy for FAP 3 years earlier. On the forward-viewing and side-viewing endoscopy done for surveillance, the overlying mucosa of the major papilla showed even granularity. On magnifying duodenoscopy using a narrow-band system (NBI), which uses modified optical filters and yields clear images of fine surface structures on the mucosal layer, a compact formation of round pits was seen in the affected ampulla. The microvascular architecture on NBI magnification showed no abnormalities, such as dilated, tortuous or network-like vessels, suggestive of malignancy. On endoscopic retrograde pancreaticocholangiography there was no intraductal growth, and endoscopic ultrasonography showed confinement to the mucosal layer. The ampullary lesion was completely resected using endoscopic snare papillectomy. Histopathological examination of the removed specimen showed tubular adenoma without malignant foci. The patient's post-treatment course was uneventful and without complications, and no local recurrence was noted on repeat endoscopy. Thus, endoscopic surveillance and removal of ampullary adenomas appear to be justified.