The presenting clinical features of a series of cases of biliary tract ascariasis are described, in particular the characteristic colicky pain which occurs. The term 'ascaritic biliary pain' is introduced for the symptom diagnostic of live Ascaris adult worms inside the biliary passages. Methods of diagnosis before, and in the course of, operation are discussed and seem adequate. The management of worms discovered in the bile ducts, and those in the proximal small bowel, is described.