Summary Diseases of small, intrahepatic bile ducts encompass a wide range of clinical conditions in adults and children, requiring a different diagnostic algorithm for each patient group. Cholestatic biliary liver disease often presents a challenge to the pathologist since there may be considerable similarities in histopathologic biopsy features and the potential for overlap syndromes. A significant number of diseases remain idiopathic, but combining clinical, radiological and morphological characteristics will generally allow the correct classification of these diseases. Aetiology, clinical presentation, prognosis, therapeutic options and liver biopsy findings are reviewed for each entity. We offer a diagnostic algorithm for both the adult and paediatric populations presenting with cholestatic liver disease.