BACKGROUND/AIMS: Endoscopic retrograde cholangiopancreatography (ERCP) is the most accurate modality in diagnosis of choledocholithiasis. However, it carries some complications. Endoscopic ultrasonography (EUS) is less invasive than ERCP and used for the diagnosis of choledocholithiasis. Recent studies showed that a usefulness of EUS for the diagnosis of small choledocholithiasis without common bile duct (CBD) dilatation. For such a reason, ERCP is being replaced by EUS in the diagnosis of bile duct stones. The aim of this study was to investigate the accuracy of EUS for the diagnosis of choledocholithiasis without CBD dilatation. METHODS: A total of 66 patients with suspected choledocholithiasis without CBD dilatation were enrolled. EUS were performed in all cases within 48 hours after computed tomography (CT) or ultrasonography (US). Final diagnosis was obtained by ERCP or clinical course (minimum 6 months follow-up). We analyzed the accuracy of US, CT, and EUS, respectively. RESULTS: CT and US were performed in 51 and 15 cases, respectively. CBD stones were detected in 23 (35%) patients by ERCP. EUS showed 100% sensitivity, 95% specificity, 92% positive predictive value, and 100% negative predictive value for identifying CBD stones. CT or US showed 26%, 93%, 67%, and 70%, respectively. There were no EUS-related complications. CONCLUSIONS: EUS was more effective than CT or US and as accurate as ERCP for the diagnosis of small choledocholithiasis without CBD dilatation. Thus, EUS may help to avoid unnecessary diagnostic ERCP and its complication.