Interstitial lung disease (ILD) has rarely been reported as a manifestation of giant cell arteritis (GCA). We herein report a unique case of GCA in a 76-year-old woman who presented with ILD as an initial manifestation of GCA. Ten years before admission, she had been diagnosed with granulomatous ILD of unknown etiology. Corticosteroid therapy induced remission. One year after the cessation of corticosteroid therapy, she was admitted with a persistent fever. After admission, she developed left oculomotor paralysis. Positron emission tomography with 2-deoxy-2-fluorine-18fluoro-D-glucose integrated with computed tomography (18F-FDG PET/CT) proved extremely useful in establishing the diagnosis. Our case promotes awareness of GCA as a possible diagnosis for granulomatous ILD with unknown etiology.