Objectives To determine prospectively the sensitivity and specificity of endoscopic ultrasound (EUS) for detecting common bile duct stones (CBS) in patients with acute biliary pancreatitis in whom transabdominal ultrasound was negative for CBS. Methods In 38 consecutive patients with acute biliary pancreatitis who were negative for CBS by transabdominal ultrasound, EUS was performed before endoscopic retrograde cholangiopancreatography (ERCP). The endoscopist performing ERCP was blind to the results of EUS. The primary goal of EUS and ERCP was to confirm or exclude CBS. The reference standard for CBS was endoscopic extraction of bile duct stones after endoscopic sphincterotomy. When both procedures, EUS and ERCP excluded CBS, it was assumed that there were no CBS and endoscopic sphincterotomy was not performed. The results EUS and ERCP were compared with the McNemar test. Results Twenty-five of the 38 patients (66%) had CBS. EUS and ERCP were false negative in one patient each, EUS was false positive in two patients and ERCP in one patient. The sensitivity of both EUS and ERCP was 96%. The specificity of EUS and ERCP was 85 and 92%, respectively. The difference between EUS and ERCP was not significant (P=0.9). Conclusion EUS proved to be as sensitive as ERCP for detection of CBS in patients with acute biliary pancreatitis. Therefore, EUS could be used as the first-line procedure in patients with acute biliary pancreatitis when therapeutic ERCP is not needed. By this approach a substantial number of unnecessary diagnostic ERCP procedures could be avoided.