OBJECTIVE: Sarcomas of the sinonasal region are rare. Histologically, this tumor most closely resembles an adult fibrosarcoma or monophasic synovial sarcoma, but shows a unique, biphenotypic staining pattern on immunohistochemistry. Differential diagnostic considerations for this neoplasm include a variety of benign and malignant mesenchymal tumors, as well as inverted a papilloma. CASE REPORT: A 55-year-old woman presented with a history of recurrent and self-limiting epistaxis of the right nasal cavity that initiated in January 2012. She denied previous episodes or other symptoms. Physical examination found a lesion that appeared to be edematous and a hypervascularized ceiling in the right nasal fossa. A nasal biopsy identified an extensively hemorrhagic spindle cell neoplasm with positive immunohistochemistry for S-100 protein expression with strong and diffuse. The patient underwent endoscopic skull base surgery. Histopathological analysis revealed a low-grade sinonasal sarcoma with neural and myogenic features. The patient opted for adjuvant chemotherapy with clinical follow-up, and had a favorable evaluation. CONCLUSION: Many of the surgical techniques described endoscopically within the skull base can be applied to malignant sinonasal disease. An endoscopic tumor surgeon should be equally comfortable managing a patient using an open craniofacial as well as an endoscopic approach. On the basis of clinical, morphologic, and cytogenetic features, we believe that this represents a distinct clinical entity that shows differentiation toward neural and myogenic cell types. Recognition of this tumor will hopefully lead to the identification of additional cases. Thus far, this tumor appears be locally aggressive and may require extensive surgery in a minority of cases to prevent recurrence.