Despite significant effort on the part of surgeons, the incidence of retained calculi after common duct exploration still remains unacceptably high. It seems likely that the best way to reduce the incidence of retained calculi would be a more complete exploration of the common duct at the time of the initial operation. We report our experience with a flexible fiber optic endoscope used intraoperatively in 52 patients and postoperatively in one case to visualize the intrahepatic and extrahepatic bile ducts. In addition to visualization of stones, the choledochoscope has a channel through which various instruments can be passed to facilitate stone removal. Flexible choledochoscopy has been performed 53 times in 52 patients between July 1978 and November 1980. In one patient, the choledochoscope was used to explore the bile ducts via the T-tube tract after operation. In 52 patients, the scope was used intraoperatively: a) two patients demonstrated bile duct tumors, b) in 14, stones were not found on exploration. Of these, one had stenosis at the papilla of Vater and one had external compression of the duct by a pancreatic pseudocyst. All of these findings were confirmed by choledochoscopy, c) in 26 patients choledochoscopy confirmed complete surgical removal of all stones, d) in six patients, multiple stones were removed using routine common duct exploration but additional stones were seen with the choledochoscope, e) in three patients no stones were retrieved on routine duct exploration but were seen using the choledochoscope. In groups (d) and (e) the scope facilitated removal of the remaining stones. In eight cases stones were either grasped or crushed using the accessories of the choledochoscope. In one patient calculi were missed both by routine surgical exploration and choledochoscopy. No septic complications were seen in any of these patients.