OBJECTIVE The clinical use of PET/CT in oncology has led to the realization that 18F-FDG uptake in brown adipose tissue (BAT)can be a common cause of potentially misleading false-positive PET scans.The goal of this study was to study 18F-FDG uptake in cervical and supraclavicular regions and its characteristics with PET/CT.METHODS All the PET/CT scans obtained at our institution from July 2007 to January 2008 were retrospectively reviewed for increased 18F-FDG uptake in BAT.The cases in which increased 18F-FDG in cervical and supraclavicular regions was not localized to a soft-tissue mass or lymph node or muscle on the CT images,were included in this study.The following features were recorded:body weight,body mass index (BMI) and maximal standardized uptake value (SUVmax).In these selected patients,the BAT uptake in other area of the body was also recorded.RESULTS PET/CT scans were obtained in 457 patients (259 males and 198 females).In all of the scans,cervical and supraclavicular BAT uptake was observed in 12 patients (2 males and 10 females) and was typically bilateral,symmetric and intense.The range of the SUVmax was 3.6～12.82 (mean 6.9 ± 2.6).BAT uptake was more common in females than in males,showing a significant difference (P = 0.004).Although 18F-FDG uptake in BAT occurred more often in underweight patients with low BMI,there was no difference in the body weight (P = 0.607) or BMI (P =0.491) of these patients with hypermetabolic BAT compared with controls.CONCLUSION Hypermetabolic BAT uptake can be localized in cervical and supraclavicular regions with it occurring more commonly in females compared to males.Knowledge of this potential pitfall with PET/CT is important in improving diagnostic interpretation and accurate staging.