PURPOSE: Bile duct dilatation after cholecystectomy continues to be a matter of controversy. We aimed determine the magnitude of common bile duct (CBD) dilatation after cholecystectomy followed up to 1 year. METHODS: Sixty-four cases (age, 47.3 +/- 11.7 years; men, 28; women, 36) enrolled in this study. They received laparoscopic cholecystectomy in Chungbuk National University Hospital for symptomatic cholelithiasis or gallbladder polyps with normal bile duct, less than 7 mm. The CBD diameter was measured by one radiologist using ultrasonography at the maximum point after full length evaluation of extrahepatic bile duct. Forty-five and thirty-one cases were followed at 6 months and 1 year, respectively. RESULTS: The CBD was dilated slightly from 4.1 mm at baseline to 5.1 mm at 6 months and 6.1 mm at 12 months after cholecystectomy. The number of cases of CBD dilatation of more than 7 mm at 6 months and at 12 months after cholecystectomy were 11 (24.4%) and 9 (29.0%), respectively. Seven cases at 6 months and 5 cases at 12 months showed bile duct dilation of more than 3 mm compared to baseline. There were no cases having bile duct dilation of more than 10 mm. CONCLUSION: Postcholecystectomy dilatation of the bile duct occured slightly in most cases. But some cases showed more than 3 mm dilatation over baseline. Asymptomatic bile duct dilatation of up to 10 mm can be considered as normal range in patients after cholecystectomy.