Background: Most patients with acute biliary pancreatitis have stones in the biliary tract or ampulla of Vater. Because these stones may be passed spontaneously soon after a patient is admitted to the hospital, the importance of early operative removal is not known. We tested the hypothesis that endoscopic papillotomy within 24 hours of admission decreased the incidence of complications in patients with acute biliary pancreatitis. Methods: We studied 195 patients with acute pancreatitis who were randomly assigned to one of two groups: 97 patients underwent within 24 hours after admission emergency endoscopic retrograde cholangiopancreatography (ERCP) followed by endoscopic papillotomy for ampullary and common-bile-duct stones, and 98 patients received initial conservative treatment and selective ERCP with or without endoscopic papillotomy only if their condition deteriorated. Results: One hundred twenty-seven patients ultimately proved to have biliary stones. Emergency ERCP with or without endoscopic papillotomy resulted in a reduction in biliary sepsis as compared with conservative treatment (0 of 97 patients vs. 12 of 98 patients, P = 0.001). The decrease in biliary sepsis occurred both in patients predicted to have mild pancreatitis (0 of 56 patients in the group that received emergency ERCP vs. 4 of 58 patients in the conservative-treatment group, P = 0.14) and in patients predicted to have severe pancreatitis (0 of 41 patients vs. 8 of 40 patients, P = 0.008). In all patients who had unrelenting biliary sepsis, persistent ampullary or common-bile-duct stones were identified. There were no major differences in the incidence of local complications (10 patients in the group that received emergency ERCP vs. 12 patients in the conservative-treatment group) or systemic complications (10 patients vs. 14 patients) of acute pancreatitis between the two groups, but the hospital mortality rate was slightly lower in the group undergoing emergency ERCP with or without endoscopic papillotomy (5 patients vs. 9 patients, P = 0.4). Conclusions: Emergency ERCP with or without endoscopic papillotomy is indicated in the treatment of patients with acute pancreatitis., That acute biliary pancreatitis is initiated by obstruction of the ampulla of Vater by migratory gallstones¹ is supported by the findings of a high incidence of stones of the common bile duct²–⁴ and impacted ampullary stones (62 to 75 percent)²,³ at operations performed within 48 hours of admission to a hospital. When surgery was delayed, the incidence of common-bile-duct stones was only 3 to 33 percent⁵,⁶ and that of impacted ampullary stones, 5 percent⁷. Persistent ampullary obstruction by an impacted stone might be responsible for the evolution of pancreatic edema to hemorrhage and necrosis². Conservative…