Fibrous dysplasia is a benign disease of unknown etiology that involves single or multiple bones. Involvement of the paranasal sinuses is rare. It can be diagnosed and differentiated from other osseo-fibrous lesions by computed tomography and magnetic resonance imaging. Its diagnosis and management often delayed until manifestation of significant clinical symptoms or non-tolerated aesthetic deformities. Surgery is the treatment of choice. We report a 44-year-old woman who presented with complaints of right-sided facial swelling, facial asymmetry and pain for one month. Coronal computerized tomography showed a heterogeneous mass of right maxillary sinus, characterized with prominent hyperdense lesion with some hypodense areas. Biopsy was performed and presumptive diagnosis of fibrous dysplasia was confirmed histologically. The patient underwent successful Caldwell-Luc removal.