Fibrous dysplasia of bone is a condition affecting one or more bones, usually not disabling, of slow progress, and showing a tendency to become arrested. The etiology of fibrous dysplaia is unknown but it is now believed to be a developmental error in which primitive fibrous tissue proliferates within the bony medulIa and encroaches upon the cortex from within, often producing expansion. The process may be localized to a small segment or may involve almost the entire shaft of the bone, and it may be monostotic, monomelic or polyostotic. In the latter form some patients exhibit a remarkable combination of skin pigmentation and endocrine disturbances. This paper reports the one case of polyostic and three cases of monostotic fibrous dysplasia. The disgnosis was made by clinical, radiological and histological findings.