A 71-year-old woman was admitted to our hospital with obstructive jaundice. Magnetic resonance cholangiography revealed a 9-cm spindle-shaped tumor in the common bile duct. Laboratory examination noted a high concentration of total serum bilirubin. Although the serum concentration of carcinoembryonic antigen was within normal limits, the serum concentration of carbohydrate antigen 19-9 was elevated. We diagnosed the lesion as an extrahepatic bile duct cancer and performed a laparotomy. The anterior wall of the common bile duct was incised, and the tumor was found to have a small base in only the posterior wall of the duct, and spread within the duct was from the common hepatic duct to the intrapancreatic bile duct. Bile duct resection, cholecystectomy with lymphadenectomy and hepaticojejunostomy were performed. Frozen sections of the proximal and distal surgical margins of the bile duct were free of cancer. Macroscopically, the lesion was an expansive polypoid tumor measuring 9x3cm in diameter arising from a 5-mm base. Histologic examination revealed that the tumor was a well-differentiated tubular adenocarcinoma that had infiltrated the fibromuscular layer at its base. Longitudinal spread was more extensive hepatopetally than hepatofugally. The patient is alive and well without any complaints 8 months after surgery.