Fibrous dysplasia (FD) is a nonhereditary benign condition in which medullary bone is replaced by immature bone and fibrous tissue. It accounts for 7% of all benign bone tumours and usually presents in the first three decades of life. FD arises from activating mutations of the GNAS gene that results in abnormal differentiation of osteoblasts. Since the mutation is somatic, clinical phenotypes range from monostotic to polyostotic FD (alone or in combination with extraskeletal findings in the skin and/or endocrine organs, a condition better known as McCune-Albright syndrome). Craniofacial region is the most involved site. Lesions usually grow slow, progress during puberty and arrest in adulthood. Management consists in following asymptomatic cases or in surgical intervention to stop progression of invalidating or obstructive lesions. The usefulness of intravenous bisphosphonate is debated. Prognosis of FD is worse in McCune-Albright syndrome, where lesions tend to relapse and to grow after puberty.