Abstract Certain definite criteria should exist before the common bile duct is opened. These are: 1. 1. Palpable stone in the hepatic or common bile ducts 2. 2. Jaundice—on admission to the hospital or recent 3. 3. Dilatation or thickening of the bile ducts 4. 4. Clinical evidence of cholangitis 5. 5. Small stones in the gall bladder 6. 6. Thickening or induration of the head of the pancreas 7. 7. Biliary colic without stones in gall bladder The presence of any one of these criteria demands choledochotomy. A small contracted gall bladder is not considered as an indication for choledochotomy nor is a history of jaundice unless its occurrence has been recent. The incidence of retained calculi in this group of patients is 5.9 per cent. In all patients the common duct was drained through a T tube or catheter. The length of time the tube remained in situ depended upon the findings at operation. Conclusions, based upon the observations of the surgeon at operation, are made upon the length of time external drainage of the hepatic and common bile ducts should be carried out.