Intrahepatic cholangiocarcinoma, which is ordinarily a very invasive tumor and often takes a rapid and fatal course, sometimes shows macroscopic intrabile duct extension. The purpose of this study is to illustrate the clinicopathologic features of this variant of intrahepatic cholangiocarcinoma, which has occasionally been reported. Five cases of the tumor with gross extension to the bile duct lumen were studied to determine their clinical and pathologic features. The tumor showed intrabile duct growth and superficial mucosal spread in two patients. In two other patients, an apparent mass lesion accompanied the intraluminal component. In the remaining patient, a polypoid tumor infiltrated the portal tract of the left lateral segment, where it had arisen. Microscopic examination did not reveal any vascular involvement or intrahepatic or lymph node metastasis. All of the patients are alive without recurrence, except for Patient 1 who died 7 years and 7 months after surgery from a rapidly growing tumor in the liver remnant. Intrabile duct growth of intrahepatic cholangiocarcinoma may reflect indolent biological behavior and thus warrants an aggressive surgical approach, which appears to give a good prognosis.