Spontaneous perforation of the extrahepatic bile duct is rare. We herein report the case of an 80-year-old woman who underwent emergency laparotomy for bile peritonitis due to a spontaneous perforation of the common bile duct. A 2-mm perforation was found in the posterior wall of the choledochus, and its wall was paper-thin. Three stones, 2mm in diameter, were removed from the common bile duct. She underwent T-tube decompression with intraoperative cholangiography demonstrating a swollen papilla of Vater. The swelling of the papilla disappeared 4 weeks after the operation. Her postoperative course was uneventful. It seems likely that the elevated intraductal pressure due to the swollen papilla following stone impaction caused the perforation in this patient. Furthermore, the excessive friability of the common bile duct of unknown etiology may also have contributed to the perforation. This experience along with a review of the literature indicate that biliary decompression is the treatment of choice for this condition.