Direct visualization of the biliary tree using choledochoscopy has been recommended as a technique to improve the accuracy of common duct exploration. In several series the incidence of retained biliary calculi has been dramatically reduced using choledochoscopy, and some authors have reported the findings of other unsuspected benign and malignant lesions as well. During an eight-year period 288 patients underwent exploration of the common bile duct specifically for calculous disease. Operative rigid choledochoscopy was performed in 140 patients in this group, with 79 found to have choledocholithiasis; seven retained stones occurred in this group for an incidence of 8.9%. Routine common duct exploration in the other 148 patients revealed 67 to have choledocholithiasis; six retained stones occurred in this group for an incidence of 9.0%. Though there was no difference in the incidence of retained stones with or without choledochoscopy, 20 patients were found to have stones missed during routine exploration once the rigid choledochoscope was inserted. In addition to the obvious value of the choledochoscope in identifying and removing common duct stones, it was also found to be an aid in removing stones in the intra-hepatic ducts and in clarifying atypical anatomy. Other causes of biliary obstruction such as a liver fluke, benign polyp, benign strictures, and ductal carcinomas were identified by use of biopsy forceps inserted through the choledochoscope. It is recommended that routine choledochoscopy be performed during common duct explorations and that surgical training programs insure that residents learn the technique of operative choledochoscopy.