The patient was a 74-year-old female presenting with abrupt onset of fever and proximal muscle pains. She had been diagnosed with polymyalgia rheumatica (PMR). On physical examination, there was no tenderness or dilatation of the temporal artery and ocular fundi were normal. 18F-FDG-PET revealed accumulation of FDG in the aorta as well as in the bilateral subclavian arteries, which strongly suggested inflammation of the large blood vessels. Magnetic resonance angiography disclosed stenosis of the bilateral subclavian arteries, which was consistent with angitis. This case was considered to have developed PMR at an old age with positive HLA DR4, and to have a complication large-vessel giant cell arteritis (LV-GCA). Administration of prednisolone at a dose of 20 mg/day promptly relieved the fever and the myalgia as well. It is difficult to diagnose GCA in PMR if no tenderness or dilatation of the temporal artery is present. FDG-PET is considered useful, not only for exploration of tumors, but also for evaluation of inflammation of large vessels.