A 66-year-old Japanese man who had undergone a subtotal gastrectomy for gastric cancer 1 year earlier, and was asymptomatic, underwent a computed tomography scan during a detailed follow-up examination, which revealed a pancreatic mass. Abdominal ultrasonography showed a solid tumor containing a cystic lesion, and abdominal magnetic resonance demonstrated a tumor with low intensity on T1-weighted images and high intensity on T2-weighted images. Although an abdominal angiography added no new information to help in establishing a preoperative diagnosis, it showed an avascular mass. An endoscopic retrograde pancreatograhy showed compression and deviation of the body part of the pancreatic duct, and dilatation of its caudal part. At laparotomy, an elastic soft tumor was found to originate from the peritoneum of the omental bursa in front of the pancreas. The tumor was encapsulated and solid. The solid lesion consisted of spindle-shaped cells, but no atypical cells were observed. The histological findings were diagnostic of a benign solitary fibrous mesothelioma, which is extremely rare. The patient is currently well and disease-free more than 5 years after this operation.