Calculous disease of the biliary system is a condition frequently encountered by the surgeon. Treatment for cholecystitis, with stones, is now a relatively easy surgical problem, and is usually followed by a result that is satisfactory to the patient. However, when the bile ducts become involved either by the passage of stones from the gallbladder into the ducts or by the formation of stones within the ducts themselves, the problem becomes more serious, both for the patient and for the surgeon. We have recently reviewed a series of 1,608 consecutive cases in which stones of the common bile duct were removed by operation at the Mayo Clinic. This number does not include 160 cases of stones in the ampulla of Vater that we have reported elsewhere. The 1,768 patients who underwent removal of stones from the common bile duct, including the ampulla of Vater, represent 13.2 per cent of all