A 64-year-old man presented with a chief complaint of abdominal pain. An abdominal computed tomography (CT) scan showed a mass 30-mm in diameter at the splenic flexure, and we diagnosed a retroperitoneal abscess. Conservative therapy was successful, and the patient was discharged. However, 1 month later, he again experienced abdominal pain. To reassess the abscess, contrast-enhanced abdominal CT was performed. In addition to the retroperitoneal abscess, the CT scan showed an approximate 30-mm mass in the head of the pancreas with no contrast uptake. The abscess was also detected by endoscopic retrograde pancreatography. We suspected but could not confirm pancreatic cancer. Two months later, the patient developed obstructive jaundice. At this time, we diagnosed pancreatic cancer, and subtotal stomach-preserving pancreaticoduodenectomy was performed. The histopathologic diagnosis was pancreatic cancer, T4, N0, M0, Stage IVa. The postoperative course was favorable, and the patient received postoperative adjuvant chemotherapy. He remains alive without recurrence 15 months after surgery.