BACKGROUND Intraductal ultrasonography (IDUS) is highly accurate in detection of extrahepatic bile duct stones. This study was to compare the accuracy of IDUS and endoscopic retrograde cholangiography (ERC) in the diagnosis of extrahepatic bile duct stones. METHODS Thirty patients suspected of extrahepatic bile duct stones on B ultrasonography, CT, or MRI were enrolled for study. ERC was performed using a Fujinon duodenoscope (ED-410XT, ED-410Xu), then IDUS was done by inserting a Fujinon microprobe (PL2220-15) through the endoscopic biopsy channel to detect the extrahepatic bile duct. Finally stones in the extrahepatic bile duct were detected and extracted by endoscopic sphincterotomy (EST). RESULTS Among the 30 patients, 26 were diagnosed as having cholelithiasis accurately through ERC. In one patient the stone detected by ERC was really floccule. Misdiagnosis happened in 2 patients with extrahepatic bile duct stones. So the overall accuracy and sensitivity of ERC in the diagnosis of extrahepatic bile duct stones were 86.7% (26/30) and 92.9% (26/28) respectively. In contrast, IDUS showed the results of diagnosis were in consistent with those of EST stone extraction. Its accuracy and sensitivity in the diagnosis of extrahepatic bile duct stones were 100% (30/30) and 100% (28/28) respectively. CONCLUSIONS IDUS which is superior to ERC in diagnosing extrahepatic bile duct stones can avoid the visual error of ERC.