Inflammatory pseudotumor is a well known but poorly understood pathologic entity. It is associated with an unusual growth of fibrotic tissue admixed with varying amounts of inflammation that displaces and compresses normal anatomic structures, resulting in dysfunction. Pseudotumors have been found in multiple locations-the orbit in particular-but to the best of our knowledge, none has previously been reported as an isolated sinus lesion. We describe a case of primary sclerosing fibroinflammatory pseudotumor of the maxillary sinus that manifested as recurrent unilateral maxillary sinusitis in a 47-year-old woman. The patient was managed with surgery and oral steroids with full resolution of her symptoms. We also review the presentation, diagnosis, and treatment of fibroinflammatory pseudotumors within the context of the current literature.