A 62-year-old man presented with pain in the upper abdomen persisting for 2 months. He had the clinical history of diabetes for approximately 10 years. CT and MRI showed a mass located in processus uncinatus of caput pancreatis. The laboratory tests, including pancreas-originated amylase, tumor marker, IgG, IgG4, and so on, were normal. For suspicion of pancreatic cancer, the patient underwent F-FDG PET/CT, which demonstrated focal and high radioactivity accumulation in processus uncinatus of pancreas, without extrapancreatic radioactivity uptake observed. Finally, the surgical pathology confirmed IgG4-related sclerosing pancreatitis.