Case description: MSSAC, female gender, caucasian, 36 year old patient. Ex-smoker and with high blood pressure condition. Reason for consultation was facial asymmetry. Both panoramic x-ray and CT scan revealed a radiopaque mass extending from the upper right central incisor to the maxillary tuberosity, with obvious maxillary sinus invasion. An incisional biopsy was performed using a trephine. The anatomo-pathological examination revealed a fibro osseous benign lesion consistent with fibrous dysplasia (monostotic). The patient, after being informed of the therapeutic options and because there was no functional or esthetic compromise, decided to monitorize the lesion and refused the surgical approach. Discussion: Fibrous dysplasia is a rare bone disease characterized by the replacement of bone with cellular fibrous tissue containing foci of ossification. In the jaws, is more frequent in the maxilla than in the mandible. Fibrous dysplasia can cause severe deformities and blindness. Some reports provided evidence that the disease becomes stabilized after bone maturation. Fibrous dysplasia should be distinguished from ossifying fibroma because both lesions often show similar histological and radiological features. Conclusion: Fibrous dysplasia is a rare and benign bone disease that can compromise aesthetically and functionally the affected individuals, especially when the craniofacial complex bones are involved. In those situations, surgical treatment is recommended in order to restore the normal anatomy of the affected structure. In the less severe cases, when skeletal growth is stabilized and no functional or aesthetical impairement occurs, the therapeutic approach would be the periodic monitorization of the bone lesions. Schlagwörter: Fibrous dysplasia, Monostotic, Maxilla, Diagnosis, Pathology