Gorham-Stout disease is a rare disorder characterized by proliferation of lymphatic and vascular channels within bone resulting in osteolysis. A 53-year-old man with Gorham-Stout disease involving the left maxilla underwent previous treatment including radiation therapy and intralesional chemotherapeutic injections. He later presented with anemia, facial pain, weight loss, and nasal cavity hemorrhage. CT imaging demonstrated a mass centered within the right maxillary sinus with locoregional involvement. PET/CT showed prominent FDG activity involving the mass centered in the right maxillary sinus with low-grade avidity involving the contralateral maxilla in regions of treated Gorham-Stout disease. Biopsy of the mass confirmed radiation-induced sarcoma.