Osteosarcoma is the most common primary malignant neoplasm of the bone. Rarely, osteosarcomas occur at sites other than the bone, so-called extraskeletal osteosarcoma (ESOS). ESOS is a rare malignancy that accounts for approximately 1% of all tissue sarcomas and present most commonly as a large soft tissue mass in the extremities. The patient was an 18-year-old Japanese man who presented with a stony hard mass in the left submandibular region. Fine-needle aspiration biopsy could not be performed due to the firmness of the mass. The patient underwent left selective neck dissection after enlargement of the mass. Three months after operation, the patient developed massive local recurrence of the tumor. We removed the tumor, encased by the muscles. Postoperatively, the patient received a course of radiotherapy. However, 4 months after the second operation, the patient developed left facial nerve palsy and complained of sudden hearing loss on the left side. The patient developed metastases and died after acute intracranial hemorrhage. To the best of our knowledge, this is the first report of a submandibular ESOS in a young man without history of radiotherapy or trauma.