Objective: Autoimmune pancreatitis (AIP) is a disease associated with various autoimmune phenomena.It is easily misdiagnosed as pancreatic cancer (PC).But the treatments of the 2 kinds of disease are very different.The purpose of this study is to evaluate the clinical utility of PET/CT in differentiating AIP from PC.Methods: 4 patients with AIP (4 male, 69±12.6) and 17 patients with PC (11 male, 5 female,68±7.6) were researched retrospectively.We compared the FDG-PET findings between the AIP and the PC visually and semi-quantitatively.The metabolic situation and the morphology of each pancreas was reviewed by 2 nuclear physicians.The SUVs and △SUVs (the change rate of the SUV in delayed image) were recorded and analyzed.Results: All of the patients demonstrated FDG accumulation in pancreas.But the AIPs showed diffused uptake, while the PCs showed localized accumulations.The SUVs of AIP (5.6±0.8)tended to be lower than the ones of PCs (8.8±5.0).16 of 17 cases of PC had SUV increased in the delayed image, while only 1 of 4 cases had increased SUV in AIP group.The △SUVs of AIPs (4%±7%) were stable compared with the ones of PCs (24%±12%).All of the differences above reached statistical significance.There were some extra-pancreatic FDG accumulations in the AIPs and PCs, such as the lung hilar and the axillary lymph nodes.But only the AIPs (2 cases) had extra-pancreatic lesions in salivary glands.Conclusions: PET/CT may be a useful tool for differentiation of AIP from pancreatic cancer.The presence of diffuse pancreatic uptake, exrtapancreatic uptake by the salivary glands and stable SUV in the delayed images may imply the diagnosis of AIP.