[ES] El mixofibrosarcoma, también denominado variante mixoide del histiocitoma fibroso maligno, se localiza predominantemente en extremidades y retroperitoneo de varones de edad adulta. Su incidencia en el área ORL es muy baja, por lo que su diagnóstico es a menudo complicado. Presenta alto índice de recidivas, aunque menor de metástasis a distancia. El único tratamiento efectivo es la resección quirúrgica completa, con escasa respuesta a quimio y radioterapia, Presentamos el caso de un mixofibrosarcoma de alto grado de seno maxilar y fosa nasal izquierdos, tratado con cirugía y quimioradioterapia con mala evolución clínica. [EN] Myxofibrosarcoma, also known as myxoid variant of malignant fibrosis histiocytoma, is often located in the extremities and retroperitoneum of adult males. Its incidence in the ENT area is very low, therefore its diagnosis is often complicated. It has a high rate of local recurrence, although it has low rate of distant metastases. The only effective treatment is complete surgical resection, with little response to chemotherapy and radiotherapy. We present the case of a high-grade myxofibrosarcoma of the left maxillary sinus and nasal cavity, wich we treated with surgery and chemoradiation, but with bad clinical evolution.