Three types of bile acid-induced diarrhoea can be distinguished. The best documented and most common entity is represented by type I bile acid malabsorption, which occurs as the result of a pathologically, anatomically defined ileopathy. Type II bile acid malabsorption is found in the setting of a morphologically completely normal ileum. This primary disorder of bile acid transport, which has been described in only a few paediatric and adult patients, appears to be rare. The third variety of bile acid malabsorption is characterized by the history of a previous cholecystectomy and/or by the presence of other gastroenterological conditions. Severe bile acid malabsorption is relatively uncommon in the type III syndrome. Even in the presence of severe bile acid malabsorption, patients with this condition are rarely found to have secretory concentrations of faecal bile acids, and/or rarely respond satisfactorily to cholestyramine. Present data suggest that bile acids play no significant role in the pathogenesis of idiopathic diarrhoea. A careful history, the measurement of stool weight and pH, a therapeutic trial of cholestyramine and the performance of a bile acid test, such as a bile acid breath test, can be used to establish the diagnosis of bile acid diarrhoea. Cholestyramine is the treatment of choice and is virtually always effective in this syndrome.