A 54-year-old female patient presented with a left nasal obstruction. On physical examination a pink delimited mass in the left nostril was observed. A cranial computed tomography scan revealed an expansive mass in the upper anterior third of the left nasal fossa, partially obstructing it. Endoscopic resection of the mass was performed. Histopathology revealed an atypical mesenchymal proliferation formed by cells disposed in disorganized and interconnected long bundles. Tumor cells had abundant eosinophilic cytoplasm and an oval, vesicular and hyperchromatic nucleus. Frequent mitotic figures were observed, many of them atypical. Necrosis was not observed. Immunohistochemistry showed tumor cells to be positive for calponin, muscle specific actin, caldesmon and smooth muscle specific myosin. Ki-67 index proliferation was 30%. A diagnosis of leiomyosarcoma of the nasal fossa was established.