OBJECTIVES: Both endoscopic retrograde cholangiopancreatography (ERCP) and endoscopic ultrasonography (EUS) are commonly performed in the evaluation of idiopathic pancreatitis. However, comparative trials of these modalities are lacking, and thus the ideal endoscopic diagnostic strategy to evaluate idiopathic pancreatitis remains unknown. METHODS: A decision analysis model of patients with 2 attacks of idiopathic pancreatitis with gallbladder in situ was constructed using TreeAge software. We analyzed cost and overall diagnostic ability of 3 strategies, namely, EUS, ERCP with manometry and bile aspiration, and laparoscopic cholecystectomy. RESULTS: Using the base case analysis, initial EUS was the preferred initial modality for the diagnosis. The expected cost for initial EUS was $4469 compared with $4615 for ERCP and $6268 for laparoscopic cholecystectomy. For cholecystectomy to be the preferred strategy, the total cost would need to be less than $1314, well below any realistic cost estimate. If the prevalence of microlithiasis/sludge was greater than 80%, then cholecystectomy would be preferred, whereas ERCP would be preferred with a prevalence of less than 41%. CONCLUSIONS: This cost minimization study identifies EUS as the least costly initial test for the diagnostic evaluation of patients with idiopathic pancreatitis with gallbladder in situ. Copyright © 2009 by Lippincott Williams & Wilkins.