Fibro-osseous lesions involving the paranasal sinuses are uncommon, and making a determination of their histologic type is challenging. Correlating clinical and surgical findings with radiologic and histologic characteristics is essential for making a definitive diagnosis. We describe a case of misdiagnosed maxillary ossifying fibroma presenting as a solitary mass that completely filled and enlarged the left maxillary sinus. Another interesting finding was the presence of a molar tooth embedded in the tumor. We briefly comment on the genesis, natural course, and differential diagnosis of this lesion.