A gallstone in the common bile duct may impact distally in the ampulla of Vater. More than 80% of gallstones contain cholesterol as their major component. If surgical removal of common bile duct stones is not immediately feasible, endoscopic retrograde sphincterotomy can be used. In this procedure, the endoscopist cannulates the bile duct the papilla of Vater. Endoscopic retrograde sphincterotomy is especially useful in patients who are critically ill with ascending cholangitis caused by impaction of a gallstone in the ampulla of Vater. A T tube is left in the duct after the procedure.