Approximately 10% of the 500,000 patients who undergo cholecystectomy for gallstones each year in the U.S.A. have associated choledocholithiasis. Of the patients who have a choledocholithotomy, 10-13% are found to have retained bile duct stones in the immediate postoperative period, and an unknown additional number are found to have biliary calculi subsequently. Residual bile duct calculi come from 3 sources, namely, "retained" stones that were overlooked during the initial operation, "retained" stones that were recognized but could not be removed at the initial operation, and "recurrent" stones that re-form in the bile ducts in association with highly lithogenic bile. Most retained stones can be prevented by knowing when and how to perform common bile duct exploration. Absolute indications, which have a high yield of calculi, are: (a) palpable stones, (b) obstructive jaundice with cholangitis, (c) demonstration of stones by cholangiography, and (d) dilatation of the common duct beyond a diameter of 12 mm. Relative indications, use of which requires judgment because of a generally low yield of calculi, are: (a) jaundice without cholangitis, (b) biliary-enteric fistula, (c) small stones in the gallbladder, (d) a single-faceted gallbladder stone, and (e) pancreatitis.Technical aspects of common duct exploration that are important for prevention of retained bile duct calculi include: (a) routine use of a Kocher maneuver, (b) routine precxploratory operative cholangiography, (c) use of the balloon-tipped catheter, (d) routine completion cholangiography through a T tube, and (e) operative biliary endoscopy. A large number of retained stones results from inadequate operative cholangiography due to poor radiographic equipment, inattention to details of technique, and insufficient collaboration between radiologist and surgeon.