Cystic dilation of the extrahepatic bile ducts is rarely encountered during elective biliary surgery planned for different indications. We report here on a patient with unremarkable preoperative workup and normal intraoperative anatomy of the cystic pedicle in whom a type I choledochal cyst containing a large stone was detected by the combined use of laparoscopic contact ultrasonography and intraoperative cholangiography. This case report highlights the importance of intraoperative imaging modalities of the ductal system not only in preventing iatrogenic injuries and their related complications, but also in detecting unsuspected associated biliary pathology which might significantly change the course of surgical intervention.