A prospective study of laparoscopic ultrasound (LUS) for evaluation of the common bile duct during laparoscopic cholecystectomy was started in October 1993. LUS during cholecystectomy was performed routinely to preoperatively identify unsuspected stones. Three-hundred thirty patients with symptomatic cholelithiasis were included in the study. The preoperative work-up included endoscopic retrograde cholangiopancreatography in 49 patients. Common bile duct (CBD) stones were found in 22 cases; in 19 cases the stones were removed successfully by endoscopic sphincterotomy. LUS successfully visualized the CBD in all but 10 patients (3%). CBD stones were found in 17 patients and confirmed by preoperative cholangiography and/or CBD exploration. There were two false-negative and one false-positive result for LUS. In 47 patients (14.2%) LUS detected CBD sludge as low-amplitude echoes without acoustic shadowing. The presence of CBD sludge was correlated with some biochemical and clinical variables. A significant correlation was identified between the absence or presence of CBD sludge and endoscopic retrograde cholangiopancreatography, acute pancreatitis, gallbladder sludge, age, and the levels of serum bilirubin and alkaline phosphatase. A significant difference was recorded between CBD diameter and the presence or absence of stones or sludge (p = 0.00001). In our experience, LUS allowed good diagnosis of CBD stones during laparoscopic cholecystectomy. The clinical significance of CBD sludge remains to be elucidated.