We describe an unusual case of biliopancreatic fistula, free perforation, and subsequent abscess formation within the lesser peritoneal sac associated with intraductal papillary mucinous carcinoma (IPMC). A 71-year-old man presented with general fatigue and loss of appetite that had persisted for 1 month. Abdominal computed tomography (CT) revealed findings consistent with an intraductal papillary mucinous neoplasm (IPMN) of the pancreas, accompanied by abscess formation in the bursa omentalis. Gastrointestinal fiberscopy revealed a swollen papilla of Vater expanded by sticky mucus, and a communication between the pancreatic duct and bile duct was demonstrated by the injection of indigo carmine solution into the pancreatic duct. Percutaneous transhepatic abscess drainage (PTAD) was performed on the day of admission. After this procedure, the patient was managed for 1 month and supported nutritionally with glycemic control for diabetes mellitus. After admission, the patient had an episode of obstructive jaundice that was treated by retrograde biliary drainage. Pancreaticoduodenectomy with lymph node dissection was then performed. Pathological examination revealed IPMN with patchy, scattered carcinoma of the pancreatic head and uncinate process with the formation of a biliopancreatic fistula. Bile duct epithelium in the area of the biliopancreatic fistula demonstrated atypical papillary epithelium suggestive of tumor invasion.