Ossifying fibroma is a rare, benign, fibro-osseous tumor of mesenchymal origin. It develops mainly in the mandible, where it is usually slow growing and asymptomatic, whereas in the maxilla and paranasal sinus, it is more aggressive. The vast majority are located in the posterior region of the mandible; however, ossifying fibroma involving the maxillary sinus is uncommon. It may reach a very large size and cause facial asymmetry. It shows a female predilection, and most cases are seen in the third and fourth decades of life. Radiographically, ossifying fibroma is radiolucent or radiopaque depending on the amount of calcification. Histologically, the tumor consists of a cementum-like or bony mass. Ossifying fibroma shares many histopathologic features with fibrous dysplasia. Their radiographic features may help to separate these entities when pathological differentiation is uncertain. It is important to differentiate ossifying fibroma from fibrous dysplasia. The treatment of ossifying fibroma involves its complete removal using curettage, enucleation, excision, or en bloc resection. This case report presents an unusual case of ossifying fibroma of the maxillary sinus. We describe a Caldwell-Luc operation with a lateral window approach for excision of an ossifying fibroma of the maxillary sinus.