Objective: This study assessed the effectiveness of laparoscopic ultrasound in detecting main biliary duct stones. Methods: From November 1994 to August 1998, 600 patients treated by laparoscopic cholecystectomy were included in a prospective study, to compare intraoperative cholangiography and laparoscopic ultrasound. The biliary tree was successively explored by these two methods in the routine detection of common bile duct stones. Results: The feasibility of laparoscopic ultrasound was 100%. Cholangiography was performed only in 498 cases (83%). The time taken for laparoscopic ultrasound examination was significantly shorter (10.2 vs 17.9 min, P=0.0001). In this study, common bile duct stones were found in 54 cases (9%). For their detection, results were comparable to laparoscopic ultrasound and intraoperative cholangiography. For laparoscopic ultrasound, sensitivity was 80% and specificity 99%; and for cholangiography 75 and 98% respectively. Both examinations combined had a 100% sensitivity and specificity. Laparoscopic ultrasound failed to recognize the intrapancreatic part of the common bile duct in 78 cases (13%) and did not show anatomical anomalies detected by cholangiography. It did however detect other unsuspected intra-abdominal pathologies. Conclusions: Laparoscopic ultrasound is safe, repeatable, and non-invasive, but a considerable learning curve is necessary to optimize its efficacy. Comparison of relative cost must be undertaken.