In two men and three women aged 64-89 years on necropsy a localized form of congenital cystic dilatation of the intrahepatic bile ducts (Caroli's disease) was found affecting the left and/or one of the segments of the right liver lobe. There was diffuse fibrosis with striking reduction of the left lobe where the dilated bile ducts were macroscopically apparent only in two subjects with concurrent occlusion of the extrahepatic bile ducts by stones and carcinoma of the head of the pancreas. Segmental dilatation of the bile ducts of the right lobe was not associated with structural changes of the hepatic tissue. On microscopic inspection the wide open or collapsed dilated bile ducts had a fibrohyaline wall of different thickness. In the smaller peripheral bile ducts there were diverticulous deformations of the lumen with persistent inflammation in the deep mucosal folds. No neuroendocrine cells or dysplastic changes were found in the mucosa and glands of the intrahepatic bile ducts.