Labeled leukocyte scintigraphy has been used as an indicator of pancreatic necrosis in patients with acute pancreatitis and proposed for the detection of infection in peripancreatic fluid collections. The authors present a PET/CT scan showing abnormal uptake of 18F-Fluorodeoxyglucose-labeled autologous leukocytes in a pancreatic pseudocyst, from which aspirated fluid subsequently showed growth of Pseudomonas aeruginosa.