Although benign and malignant tumors of the major duodenal papilla can be detected endoscopically, definitive diagnosis of such lesions by histologic examination of biopsy specimens is sometimes difficult, especially in cases with intraductal extension into the bile duct or pancreatic duct. We herein report a case of adenoma of the major duodenal papilla showing an intraductal extension into the lower common bile duct that necessitated pylorus-preserving pancreaticoduodenectomy.