Eleven patients with chronic intrahepatic cholestasis in whom a liver biopsy specimen showed unexplained bile duct paucity were investigated. Cholestasis developed during the neonatal period in three, at infancy (before 14 yr) in four and after 14 yr in the remaining four patients. In all patients other conditions characterized by chronic cholestasis associated with ductopenia such as primary biliary cirrhosis, primary sclerosing cholangitis, drug-induced liver disease, sarcoidosis or graft-vs.-host disease were excluded. Cardiovascular abnormalities in the three patients who had neonatal cholestasis permitted diagnosis of Alagille's syndrome. Clinical, biochemical and histological features were similar in the remaining eight patients, independent of the age at which the disease appeared. Idiopathic adulthood ductopenia may be a late-onset form of the nonsyndromic paucity of interlobular bile ducts seen in children, or it may be due to a still-unidentified cause that strikes later in life.