BACKGROUND: Endoscopic retrograde cholangiopancreatography (ERCP), with or without sphincterotomy, has been widely used in patients with severe biliary acute pancreatitis (BAP) or those with cholangitis and/or obstruction of the biliary tree. Its use in subjects with mild BAP is more controversial. AIM: To optimize use of ERCP in patients with mild pancreatitis due to gallstones by identifying clinical and biochemical predictors of choledocholithiasis. MATERIAL AND METHOD: The clinical and biochemical data, images, and outcomes of 83 patients with mild BAP hospitalized at the Instituto Nacional de Ciencias Medicas y Nutricion "Salvador Zubiran" from January 1, 1988 to May 30, 2000 were retrospectively analyzed. All patients received elective cholecystectomy at hospital admission. In 35 cases, ERCP was performed before cholecystectomy (group A). The remaining 48 were operated on without ERCP (group B). In 30, transcystic-cholangiography was done. Forty-seven (57%) were female. Mean age was 47 years (19-90). Mean time between onset of AP and hospital admission was 2.2 days (1-15), and between clinical onset and cholecystectomy, eight days (1-26). Statistical differences were evaluated by non-parametric methods. An univariated and multivariated analysis was performed looking for data to identify choledocholithiasis. RESULTS: Choledocholithiasis was found in 27 cases (32%), 18 from group A (51%), and nine for group B (19%) (RR = 4.58, IC 95% = 1.7-12.25, p = 0.004). ERCP was performed in all cases because of clinical suspicion of choledocholithiasis (jaundice, bilirubin, and alkaline phosphatase alteration and/or choledochal dilation); however, none of the patients of group B in whom choledocholithiasis was operatively diagnosed showed biochemical or radiologic alterations. Subjects with choledocolithiasis presented more frequently a history of biliary pain (RR = 5.75, IC 95% = 1.76-18.7), jaundice (RR = 3.07, IC 95% = 1.15-8.16) and/or alkaline phosphatase elevation (RR = 4.11, IC 95% = 1.3-12.7). CONCLUSION: The high frequency of choledocholithiasis in subjects with mild biliary pancreatitis warranted radiologic exploration of the biliary tree in all patients submitted to cholecystectomy. In those with jaundice, alkaline phosphatase elevation and/or a history of biliary pain, ERCP should be performed prior to the operation; in others, choledocholithiasis can be discharged by operative transcystic cholangiography. Therapeutic measures for treating choledocholithiasis should be adapted to hospital facilities.