The case of 4-month-old female with choledocholithiasis associated with bile duct perforation and biloma is reported. She was a premature infant weighing 1432 g at birth. She underwent an ultrasonographic examination because of fever and abdominal distension. It revealed an anechoic cyst, 5×5×4cm in size, which was localized in the right upper quadrant of the abdomen. A 99mTC-PMT biliary scan demonstrated a cyst in communication with the bile duct. At laparotomy, a cyst was located in the area bounded by the duodenum, the gallbladder and the surface of the common bile duct. The cyst was opened and a small bile duct perforation through which bile was leaking was found at the bottom of the cyst, just below the entrance of the cystic duct. Intraoperative cholangiography showed no dilation of the common bile duct (4 mm in diameter) and free bile drainage into the duodenum. After incision of the bile duct, 2 small pigment stones were flushed out by irrigation with saline. From to the above, we considered the cyst a biloma caused by bile duct perforation. Retrograde transhepatic biliary drainage was perforation, followed by primary closure of the common bile duct. She has remained asymt omatic for 20 months after the operation.