We herein report the first case of a pancreatic fistula extending into the thigh caused by the rupture of an intraductal papillary mucinous neoplasm (IPMN) of the pancreas. An 80-year-old man was suspected to have necrotizing fasciitis because of right femoral pain. Computed tomography showed fluid retention from the pancreatic head to the right iliopsoas muscle and an IPMN at the pancreatic head. The findings of endoscopic retrograde pancreatography led to the suspicion of a minor leak and a pancreatic stent was placed. The patient died due to an uncontrollable infection. A pathological autopsy showed a pancreatic fistula extending into the thigh that had been caused by the rupture of the IPMN.