A 7-year-old girl underwent laparotomy for suspected acute appendicitis. Instead, bile peritonitis with hydrops of gallbladder and normal appendix were noted. Dilatation of the CBD was observed, and choledochal cyst was documented by intraoperative cholangiography. Cholecystectomy and T-tube placement were performed. Postoperative follow-up by ultrasound lasted for 9 months. The CBD remained the same size without clinical manifestation.