We present a rare case of adenomyomatous hyperplasia of the extrahepatic biliary system and describe the histologic features. We performed a pyloruspreserving pancreatoduodenectomy in a 62-year-old man in whom carcinoma of the bile duct was strongly suspected on histologic examination. Gross appearance of the resected specimen revealed an elevated nodule at the terminus of the common bile duct, measuring 20 × 15 × 4 mm. Histologic examination revealed fibrous thickening of the wall in the distal bile duct along with proliferation of both epithelial and smooth muscle components and moderate infiltration by inflammatory cells. The epithelial components were arranged in a lobular fashion comprised of larger ducts, smaller ductules, smooth muscle fibers, and fibrous connective tissue. Since this lesion resembled an adenomyoma or adenomyomatous hyperplasia of the papilla of Vater, we considered it to be a case of adenomyomatous hyperplasia of the common bile duct.