There are very few benign or malignant diseases which arise in the remnant pancreas after pancreatectomy. Pancreatic carcinoma in the remnant pancreas after pylorus preserving pancreatoduodenectomy (PpPD) for mucinous cystadenoma in a 66-year-old Japanese man is reported in this paper. The patient underwent PpPD for a mucinous cystadenoma in the pancreatic head 39 months prior to the present operation. The surgical margins of the PpPD specimen were free from atypical cells. Follow-up ultrasonography revealed a hypoechoic lesion in the body of the remnant pancreas. Magnetic resonance cholangiopancreatography (MRCP) revealed a stenosis of the main pancreatic duct, with upstream dilatation in the remnant pancreas. Segmental resection of the remnant pancreas, splenectomy, pancreaticojejunostomy and intraoperative radiotherapy were performed under the diagnosis of pancreatic carcinoma of the remnant pancreas. Final histopathological diagnosis was adenocarcinoma of the pancreas. There were no malignant cystic components. The present pancreatic carcinoma was regarded as independent of the previous mucinous cystadenoma. Postoperative radiation therapy and chemotherapy were added. He is doing well 20 months after the second operation although diabetes mellitus has slightly deteriorated. In this communication, we would like to recommend that clinicians should constantly be on guard against the development of pancreatic carcinoma even in the remnant pancreas after pancreatectomy for mucinous cystadenoma.