AbstractBackground.We report a rare case of endodermal sinus tumor (EST) of the paranasal sinus in a 59‐year‐old man with a 6‐week history of nasal obstruction.Methods and Results.High‐resolution MRI showed a right nasoethmoid mass with obstructive changes in the sphenoid, frontal, and right maxillary sinuses and orbital and intracranial extension. Histologic analysis showed 2 distinct histologic features: poorly differentiated carcinoma and EST. Immunohistochemical studies showed strong keratin staining in both components and restricted positivity of α‐fetoprotein in the endodermal sinus‐like component. The patient underwent 3 cycles of neoadjuvant chemotherapy consisting of ifosfamide, paclitaxel, and cisplatin, which resulted in significant regression of the tumor, but after the fourth cycle, the mass showed a slight increase in size. The tumor was excised with clear margins through an anterior craniofacial approach to the skull base. Histologic examination of the resected specimen showed extensive fibrosis with residual areas of viable tumor composed mainly of the poorly differentiated component with only residual microscopic foci of EST. Adjuvant postoperative intensity‐modulated radiation therapy was administered. At 1‐year follow‐up, the patient was tumor free, with normal α‐fetoprotein levels.Conclusion.Because of the rarity of this entity, no standardized treatment protocol has been defined. The involvement of the anterior skull base in our case necessitated a radical craniofacial resection, despite a partial response to chemotherapy. © 2007 Wiley Periodicals, Inc. Head Neck, 2008