rare congenital developmental disorder beginning in childhood and characterized by replacement of solid calcified bone with fibrous tissue, often only on one side of the body and primarily in the long bones and pelvis. One bone (monostotic) or several bones (polystotic) may be affected. The disease appears to result from a genetic mutation that leads to the overproduction of fibrous tissue. Manifestations of the disorder include enlargement of the bones on one side of the face and base of the skull, bone pain, and a tendency to fractures (fracture). Individuals with fibrous dysplasia who exhibit café au lait (pale brown) spots on the skin and endocrine imbalance leading to precocious puberty, especially in girls, have a form of the disorder called McCune-Albright syndrome. Orthopedic surgery may be necessary for disability resulting from fractures and bony overgrowth.