Computer-assisted three-dimensional (3D) reconstruction of the biliary tree including extrahepatic and intrahepatic parts was performed from surgical or autopsy materials from 12 patients with hepatohilar bile duct carcinoma in an effort to visualize three-dimensionally the distribution of carcinoma and dysplasia. In each case, material including a hepatic lobe was reduced to serial slices 1 mm thick using a ham slicer, then the tumors, ducts with carcinoma in situ, and those with dysplasia were submitted to reconstruction. In a 3D map of biliary tree reproduced on a display, a dysplastic zone was shown in most cases surrounding a focus of carcinoma, justifying the assumption of a dysplasia-carcinoma sequence. The carcinoma itself proved to form multiple foci along bile ducts in as many as 42% of the patients, in some of whom the foci were independent without any intervening dysplasia. These results suggest that as extensive a surgical measure as possible should be taken in designing a strategy against this tumor.