Experience with nine cases indicates that fibrous dysplasia of bone may present a variable clinical picture. In adults there may be rather extensive lesions in more than one bone without symptoms or serious impairment of function. The solitary lesions respond to curettage and packing with bone chips, but this procedure was not beneficial in treating large lesions, where the abnormal tissue could not be entirely removed. In the usual case a summation of clinical, roentgenographic, and microscopic findings is desirable for diagnosis of this disease. When islands of cartilage are present, the diagnosis can be made on the basis of the gross or microscopic examination alone.