Extrahepatic bile duct carcinoma occasionally presents with intraepithelial spread for a considerable area around the main tumor. In this study, we compared clinicopathological features of extrahepatic bile duct carcinoma with and without extensive intraepithelial spread (>or=20 mm from the main tumor). Out of 117 cases of extrahepatic bile duct carcinoma, 21 (18%) were found to have extensive intraepithelial spread. Those cases were pathologically characterized by a papillary or nodular main tumor, a more differentiated histological grade, less deep invasion, and infrequent portal vein or hepatic invasion in comparison with cases without intraepithelial spread. Areas of intraepithelial spread histologically consisted of low-papillary growth (17 cases, 81%) and completely flat growth (4 cases, 19%) of carcinoma cells. The former histology corresponded to a macroscopic granular mucosa, whereas the latter growth was hardly detected by gross examination. Immunohistochemically, in 16 of 21 cases (76%), at least one of p53, CEA, and MUC1 was expressed in both the main tumor and the spreading area. Interestingly, patients with intraepithelial spread had a better postoperative prognosis than those without intraepithelial spread (P=0.009). However, three patients had anastomotic recurrence 54-130 months after surgery. In conclusion, intraepithelial-spreading bile duct carcinoma is characterized by papillary or nodular main lesions, a more differentiated histological grade, and less invasiveness. The presence of intraepithelial spread was not an indicator of a poor prognosis, but carcinoma in situ at the bile duct stump could cause late anastomotic recurrence after surgery.