Sinonasal teratocarcinosarcoma (SNTCS) is an extremely rare malignancy of the paranasal sinuses that possesses the histopathologic features of both teratomas and carcinosarcomas. We report the case of a 58-year-old white man who presented with a 1-year history of a gradually enlarging left-sided nasal mass. The patient had previously undergone endoscopic sinus surgery at another facility, and the final pathologic specimen was reported as an SNTCS with positive margins. He was then referred to our institution, where he underwent a craniofacial resection combined with endoscopic intranasal resection. Postoperatively, he received combined chemotherapy and irradiation. At 48 months of follow-up, he was alive without evidence of disease.