Background: One of the most reliable, frequently used imaging techniques in cholestasis is ultrasonography (US) for the diagnosis of common bile duct (CBD) stones. Methods: In this study, changes in diameters of CBD were determined ultrasonographically before and after endoscopic sphincterotomy (ES) in 46 patients with stone-induced dilated CBD. Results: There was a significant decrease in CBD diameter measured 1 week after ES and extraction of stone (p < 0.001). In 87% of cases, the difference was more significantly pronounced during the first 24 h of ES. The mean CBD diameters on US were 13.70 ± 3.00 mm (10–21 mm) before and 9.13 ± 2.90 mm (4.2–18 mm) 24 h after endoscopic treatment (p < 0.001). After ES, six patients (13%) with inadequate decreases in CBD diameters were found to have residual stones. Conclusion: US can show residual stones in the CBD with the same efficacy as endoscopic retrograde cholangiopancreatography.