In this paper, we report a case of maxillary osteosarcoma which was suspected to be radiation-induced cancer. The patient, a 67-year-old male, received 35 Gy of 60Co external beam, 2, 000 mg of 5-FU via the superficial temporal artery and an antrostomy at another hospital in 1977. In, 1986, nine years after the radiotherapy, a maxillary osteosarcoma arose in the irradiated field. The possibility of radiation-induced osteosarcoma is very high, because the tumor is categorized into group A of Sakai, et al. definition of induced cancer. Gastric cancer was also concurrently present. In spite of the operation, he died of recurrent gastric cancer and liver metastasis. It was suggested that double cancers involving the gastrointestinal system should be surveyed in cases of head and neck cancer.