BACKGROUND: Endosonography (EUS) and endoscopic retrograde cholangiopancreatography (ERCP) are highly accurate techniques for evaluating common bile duct stones. AIM: To compare the clinical impact and costs of EUS- and ERCP-based strategies for evaluating patients with suspected common bile duct stones but normal transabdominal imaging. METHODS: The costs of EUS- vs. ERCP-based strategies were compared in patients with suspected acute biliary obstruction from common bile duct stones but normal transabdominal imaging. RESULTS: Over a 15-month period, 110 patients were recruited. EUS detected a common bile duct lesion in 73% (common bile duct stones: 68%; pancreatic cancer: 2%; ampulla tumour: 2%; cholangiocarcinoma: 1%). The sensitivity, specificity, positive predictive value and negative predictive value of EUS were 98%, 100%, 100% and 93%, respectively. EUS prevented 30% unnecessary ERCP. The mean difference in cost per patient between EUS- and ERCP-based strategies was US$166. When stratified according to clinical indications, an EUS-based strategy was costlier only in suspected biliary sepsis. Costs were similar when the indications were cholestatic jaundice, acute pancreatitis and cholestasis. CONCLUSION: EUS prior to biliary interventions in patients with suspected common bile duct stones prevented unnecessary ERCP. It allowed a definitive diagnosis to be made prior to more invasive procedures.