Dilatation of the intrahepatic biliary tree without mechanical obstruction and sometimes with similarly unexplained dilatation of the common bile duct may occur as an isolated developmental abnormality (Caroli's syndrome) or as part of one of a number of rare conditions. These are considered in relation to five patients seen during the past two years. Four were finally proven, on liver biopsy, to have congenital hepatic fibrosis although their initial presentation was with cholangitis which was poorly controlled by antibiotics and eventually led to death in three of them. Surgical attempts to improve biliary drainage in two patients were unsuccessful; this experience together with review of the rare cases in the literature suggests that surgery is only indicated when, as a result of stasis in the dilated biliary tree, calculi form and cause mechanical obstruction. Consistent with the diagnosis of congenital hepatic fibrosis was the finding in three patients of renal abnormalities. The pyelographic appearances in two cases were identical with medullary sponge kidney, although there are important clinical and pathological differences from the usual form of this condition. In the fifth patient, with a long history of portal hypertension dating from childhood, the intrahepatic bile duct dilatation was associated with gross atrophy of the left lobe and the ducts were filled with pus at autopsy. One closely similar case was found in a detailed search of the literature.