OBJECTIVE To describe characteristics of a poorly expandable (PE) common bile duct (CBD) with stones on endoscopic retrograde cholangiography. METHODS A PE bile duct was characterized by a rigid and relatively narrowed distal CBD with retrograde dilatation of the non-PE segment. Between 2003 and 2006, endoscopic retrograde cholangiography (ERC) images and chart reviews of 1213 patients with newly diagnosed CBD stones were obtained from the computer database of Therapeutic Endoscopic Center in Chang Gung Memorial Hospital. Patients with characteristic PE bile duct on ERC were identified from the database. Data of the patients as well as the safety and technical success of therapeutic ERC were collected and analyzed retrospectively. RESULTS A total of 30 patients with CBD stones and characteristic PE segments were enrolled in this study. The median patient age was 45 years (range, 20 to 92 years); 66.7% of the patients were men. The diameters of the widest non-PE CBD segment, the PE segment, and the largest stone were 14.3 ± 4.9 mm, 5.8 ± 1.6 mm, and 11.2 ± 4.7 mm, respectively. The length of the PE segment was 39.7 ± 15.4 mm (range, 12.3 mm to 70.9 mm). To remove the CBD stone(s) completely, mechanical lithotripsy was required in 25 (83.3%) patients even though the stone size was not as large as were the difficult stones that have been described in the literature. The stone size and stone/PE segment diameter ratio were associated with the need for lithotripsy. Post-ERC complications occurred in 4 cases: pancreatitis in 1, cholangitis in 2, and an impacted Dormia basket with cholangitis in 1. Two (6.7%) of the 28 patients developed recurrent CBD stones at follow-up (50 ± 14 mo) and were successfully managed with therapeutic ERC. CONCLUSIONS Patients with a PE duct frequently require mechanical lithotripsy for stones extraction. To retrieve stones successfully and avoid complications, these patients should be identified during ERC.