Giant cell tumor (GCT) is a generally benignbone tumor accounting for approximately 5 % of all primarybone neoplasms. Cystic components in GCTs thatindicate secondary aneurysmal bone cysts (ABCs) are reportedin 14 % of GCTs. Although both of them havebeen described separately in previous reports that mayshow considerable fluorodeoxyglucose (FDG) uptake despitetheir benign nature, the findings of GCT with secondaryABC on 18F-FDG positron emission tomography/computed tomography (PET/CT) have not been wellknown. We report a case of GCT with secondary ABCin a 26-year-old woman. 18F-FDG PET/CT revealed aheterogeneous hypermetabolic lesion in the left proximalfemur with the maximum standardized uptake value of4.7. The solid components of the tumor showed higherFDG uptake than the cystic components. These observationssuggest that the ABC components in GCTs showheterogeneous metabolic patterns on 18F-FDG PET/CT.