A 67-year-old man with back pain was diagnosed as having multiple spinal metastases on MRI. On CT scan, only a filling defect in the right pulmonary artery was observed and suspected as venous thromboembolism. On F-18 fluorodeoxyglucose (FDG) PET/CT, intense hypermetabolism was observed in the right pulmonary artery in addition to the metastatic spine lesions. Biopsy confirmed the lesion as a primary pulmonary artery sarcoma (PAS), and the spine lesions as metastases of PAS. Although PAS is rare and its bone metastasis presenting initial symptom is extremely rare, FDG PET/CT is an effective diagnostic modality for PAS, not only in discrimination from venous thromboembolism, but also in workup of metastatic origin.