A 52-year-old man with intermittent head motor tics, aphasia and right upper extremity weakness had an 18F-FDG avid left front lobe brain lesion, and a left upper lobe lung lesion on PET/CT. The brain lesion was surgically resected, and was diagnosed pathologically as a histiocytic sarcoma (HS). The lung lesion was also a HS via bronchial biopsy. HS is rare and generally involves nodes as shown on PET/CT in a few case reports. The current case with simultaneous brain and lung HS lesions adds new imaging pattern information of the disease to the literature.