BACKGROUNDTechniques for diagnosing choledocholithiasis pose significant morbidity and mortality risks.OBJECTIVESWe aimed to develop and validate a clinical scoring system for predicting choledocholithiasis.DESIGNData from a prospectively maintained database of all patients with gallstones.SETTINGPatients were admitted to the general surgery department of a military hospital.PATIENTS AND METHODSWe enrolled consecutive patients with symptomatic gallstones, biliary pancreatitis, obstructive jaundice, or cholangitis, who subsequently underwent biochemical testing and ultrasonography. A predictive model was developed from a scoring system using their imaging and laboratory data. Endoscopic retrograde cholangiopancreatography (ERCP) or intraoperative cholangiography were used for confirmatory diagnoses. The predictive efficacy of the scoring system was validated using a retrospective cohort of 272 patients.MAIN OUTCOME MEASURESPredictive accuracy of the scoring system.RESULTSWe enrolled 155 patients in the development group. The common bile duct diameter, alkaline phosphatase of ≥200 IU, elevated bilirubin levels, alanine transaminase of ≥220 IU, and male age of ≥50 years were significantly associated with choledocholithiasis and were included in the scoring system. Ninety-six patients (35%) had scores of ≥8 (high risk), 86 patients (32%) had scores of 4–7 (intermediate risk), and 27 patients (10%) had scores of 1–3 (low risk). In the validation cohort, the positive predictive value for a score of ≥8 was 91.7%, and the scoring system had an area under the curve of 0.896.CONCLUSIONScores of ≥8 were strongly correlated with choledocholithiasis in the developmental and validation groups, which indicates that our scoring system may be useful for predicting the need for therapeutic ERCP. However, prospective validation in a large multicenter cohort is needed to fully understand the benefits of the system.LIMITATIONSThe retrospective validation cohort might have introduced selection and observational biases. The study may have been underpowered because of the sample size of the developmental cohort. The delay between admission and the time of ERCP theoretically may have increased the number of negative ERCP results, but our false negative rate for ERCP was consistent with the previously reported rates.