Residual calculi following cholecystectomy may be expected in approximately seven percent of cases. The vast majority of these are overlooked during operation; truly re-formed stones are rare. Calculi are missed during cholecystectomy because of failure to explore the common bile duct. This is due to (1) the presence of silent choledochal stones, and (2) reliance on negative cystic duct cholangiograms in the presence of indications for common duct exploration. Overlooking of silent stones during cholecystectomy may be prevented by routine operative cholangiography. Ideally, false-negative cystic duct cholangiograms should be eliminated by the use of fluoroscopic cholangiography. Retained calculi following duct exploration may be prevented by (a) routine biliary endoscopy and (b) completion fluoroscopic cholangiography.Re-formation of ductal calculi can probably be prevented by appropriate biliary drainage procedures performed during the initial choledochotomy. Selection of patients for primary biliary decompression remains an experimental problem.