Objectives-To evaluate changes in the common duct diameter on sonography over time in patients with and without cholecystectomy. Methods-We retrospectively evaluated the common duct diameter, central biliary dilatation, and interval change in 1079 patients who underwent sonography at least 2 years apart over a 6-year period. A board-certified radiologist, blinded to clinical and laboratory data, measured the duct diameter. A total of 893 patients (568 female and 325 male) were divided into 3 groups: group 1, remote cholecystectomy before sonography (mean, 9.7 years before sonography; n = 117); group 2, interval cholecystectomy between the first and second sonographic examinations (n = 56); and group 3, no cholecystectomy (n = 720). All groups were stratified by age, and group 3 was also stratified by the absence (n = 528) or presence (n=192) of gallstones. Results-Duct diameters at baseline and follow-up averaged 4.5 and 5.2, 3.6 and 4.9, and 3.5 and 3.9 mm in groups 1, 2, and 3, respectively. Group 1 ducts were larger at baseline than in the other groups (P< .001). At follow-up, group 2 ducts showed a greater interval diameter increase than the other groups (P < .001). In a subanalysis of each group based on age, there was a mild increase in duct size with increasing age, although not clinically significant and within normal limits. In group 3 patients who never had gallstones, there was a significant small increase in duct size over decades (P < .001). The baseline duct sizes for patients with gallstones were not significantly different from those who never had gallstones (P = .15). Conclusions-Patients with remote cholecystectomy have larger common duct diameters than those with no or interval cholecystectomy. Most asymptomatic patients with or without cholecystectomy have a normal common duct diameter. © 2013 by the American Institute of Ultrasound in Medicine.