Post-endoscopic retrograde cholangiopancreatography pancreatitis (PEP) is the most common adverse event after endoscopic retrograde cholangiopancreatography, and is responsible for substantial morbidity and health care expenditures of at least $200 million. Therapies for PEP prevention include pancreatic stent placement (PSP), rectal indomethacin, sublingual nitrates, and aggressive lactated Ringer's hydration. Our objective was to determine which PEP prophylactic strategies are cost effective. We developed 2 separate decision trees to evaluate PEP prophylactic strategies. The first, in high-risk patients, compared rectal indomethacin, PSP, PSP with indomethacin, sublingual nitrates, aggressive hydration with lactated Ringer's, and no prophylaxis. The second, in average-risk patients, compared rectal indomethacin, sublingual nitrates, aggressive hydration, and no prophylaxis. We used incidence rates, transition probabilities, and costs from publications and public data sources. Outcome measures were reported as incremental cost-effectiveness ratios, with a willingness-to-pay (WTP) threshold of $100,000/quality-adjusted life years (QALYs). Compared with no prophylaxis, all strategies were cost effective at a WTP of $100,000 in preventing PEP in high-risk patients. When directly compared with each other, rectal indomethacin was the cost-effective strategy in high-risk patients ($31,589/QALYs). In average-risk patients, indomethacin and sublingual nitrates were cost effective at a WTP of $100,000/QALYs compared with no prophylaxis. When directly compared with each other, rectal indomethacin was the cost-effective strategy ($53,016/QALYs). Rectal indomethacin was the cost-effective strategy for preventing PEP in both average-risk and high-risk patients undergoing endoscopic retrograde cholangiopancreatography. All strategies were cost effective when compared with no prophylaxis in high-risk patients, whereas all strategies except for aggressive hydration with lactated Ringer's were cost effective in average-risk patients. Further studies are needed to improve the utilization of PEP prevention strategies.