18F-fluorodeoxyglucose positron emission tomography (18F-FDG-PET) has been used as a potential tool for imaging nodal follicular lymphoma (FL) and extranodal spread. As primary intestinal FL is increasingly being recognized, we have performed a study to investigate the usefulness of 18F-FDG-PET for staging of extranodal FL within the gastrointestinal tract. In eight patients with a diagnosis of FL localized in the duodenum (six cases in stage I and one each in stages II and IV, respectively) whole body 18F-FDG-PET scans were performed. Seven patients with duodenal FL were rated WHO grade 1 and one had FL grade 3, while both patients with secondary spread had FL WHO grade 1. All patients were imaged before initiation of therapy. None of the patients with primary duodenal FL showed pathologically elevated 18F-FDG uptake. 18F-FDG-PET findings were not influenced by histological grade or proliferative activity of FL. These findings suggest that 18F-FDG-PET is not useful for clinical assessment of primary duodenal FL.