OBJECTIVE To detect and manage residual common bile duct (CBD) stones using ultraslim endoscopic peroral cholangioscopy (POC) after a negative balloon-occluded cholangiography. METHODS From March 2011 to December 2011, a cohort of 22 patients with CBD stones who underwent both endoscopic retrograde cholangiography (ERC) and direct POC were prospectively enrolled in this study. Those patients who were younger than 20 years of age, pregnant, critically ill, or unable to provide informed consent for direct POC, as well as those with concomitant gallbladder stones or CBD with diameters less than 10 mm were excluded. Direct POC using an ultraslim endoscope with an overtube balloon-assisted technique was carried out immediately after a negative balloon-occluded cholangiography was obtained. RESULTS The ultraslim endoscope was able to be advanced to the hepatic hilum or the intrahepatic bile duct (IHD) in 8 patients (36.4%), to the extrahepatic bile duct where the hilum could be visualized in 10 patients (45.5%), and to the distal CBD where the hilum could not be visualized in 4 patients (18.2%). The procedure time of the diagnostic POC was 8.2 ± 2.9 min (range, 5-18 min). Residual CBD stones were found in 5 (22.7%) of the patients. There was one residual stone each in 3 of the patients, three in 1 patient, and more than five in 1 patient. The diameter of the residual stones ranged from 2-5 mm. In 2 of the patients, the residual stones were successfully extracted using either a retrieval balloon catheter (n = 1) or a basket catheter (n = 1) under direct endoscopic control. In the remaining 3 patients, the residual stones were removed using an irrigation and suction method under direct endoscopic visualization. There were no serious procedure-related complications, such as bleeding, pancreatitis, biliary tract infection, or perforation, in this study. CONCLUSIONS Direct POC using an ultraslim endoscope appears to be a useful tool for both detecting and treating residual CBD stones after conventional ERC.