We present the (18)F-FDG PET/CT images of a 38-year-old woman with primary pericardial osteosarcoma. Routine chest radiography showed an enlarged cardiac silhouette. Plain chest CT found an oval tumor with dense calcification adhered to the left back of the heart. A whole-body FDG PET/CT scan was performed to evaluate the patient's condition. The images showed heterogeneous tracer uptake in the calcified tumor. There was no other evidence of active neoplastic disease. Histopathologic analysis of the pericardial tumor showed characteristic findings of primary pericardial osteosarcoma.