Fibrous dysplasia is an abnormal bone growth where normal bone is replaced with fibrous bone tissue. Fibrous dysplasia causes abnormal growth or swelling of bone. Fibrous dysplasia can occur in any part of the skeleton but the bones of the skull, thigh, shin, ribs, upper arm and pelvis are most commonly affected. Fibrous dysplasia is very rare, and there is no known cure. Fibrous dysplasia is not a form of cancer. Most lesions are monostotic, asymptomatic and identified incidentally and can be treated with clinical observation and patient education. This disorder is usually diagnosed in childhood or early adulthood and can affect one or several bones. Males and females of any race are equally affected.