The usefulness of positron emission tomography-computed tomography (PET-CT) with 18 F-labeled fluorodeoxyglucose (18 F-FDG) for the diagnosis of lymphoma in patients with primary Sjögren's syndrome (SS) is unclear, since the abnormalities it reveals may be due to systemic manifestations of SS. This study was undertaken to compare 18 F-FDG-PET-CT in patients with primary SS with lymphoma and those without lymphoma in order to identify patterns associated with lymphoma.