Radiation therapy is frequently used method in treatment of the head and neck malignancies. Osteosarcoma is a rare complication of radiation therapy and usually occurs after a long latent period. We report the case of 75-year-old female with osteosarcoma of the mastoid process. Twelve years before presentation she received radiation therapy after total parotidectomy and radical neck dissection in treatment of mucoepidermoid carcinoma of the parotid gland. Diagnostic procedures included contrast-enhanced CT and MRI of the head and neck and HRCT of the temporal bone. The final diagnosis of the low grade osteosarcoma was confirmed by biopsy. Diagnostic criteria were fulfilled and the lesion was classified as a radiation induced osteosarcoma.