OBJECTIVES: The role of ERCP in acute biliary pancreatitis (ABP) is controversial. Magnetic resonance cholangiopancreatography (MRCP) and endoscopic ultrasonography (EUS) are modalities for bile duct visualization that could lower costs and prevent ERCP-related complications. We analyzed costs and examined the cost-effectiveness of these modalities to define their role in ABP. METHODS: A decision analysis model of ABP was constructed. The strategies evaluated were 1) ERCP, 2) MRCP followed by ERCP if positive for common bile duct stones (CBDS) or if biliary sepsis ensued, 3) EUS followed by ERCP if positive or if biliary sepsis ensued, and 4) observation with intraoperative cholangiography at the time of cholecystectomy with ERCP only if biliary sepsis ensued. We compared costs and performed cost-effectiveness analysis between strategies at probabilities of CBDS ranging from 0% to 100%. The outcome measures were total costs and costs per ABP death prevented. RESULTS: At probabilities of CBDS <15%, observation with intraoperative cholangiography is the least expensive strategy, whereas EUS and ERCP are the least expensive strategies at probabilities of 15-58% and >58%, respectively. In terms of cost-effectiveness, at probabilities of CBDS of 7-45%, EUS is the most cost-effective alternative, and at a probability of >45% ERCP is the most cost-effective option. CONCLUSIONS: Total costs and cost-effectiveness ratios of these strategies in patients with ABP are highly dependent on the probability of CBDS. © 2001 by Am. Coll. of Gastroenterology.