A 37 year-old female patient with polyostotic fibrous dysplasia (PFD) is described. She presented the typical "café au lait" spots and severe bone involvement including a maxillary osteosarcoma. The father, four sibs, two nephews, two paternal aunts and two paternal first cousins were clinically examined, and seven of them also radiologically evaluated. "Café au lait" spots were found in the father, three sibs, one nephew, one aunt and one first cousin. Although no definite PFD bone lesions, mild radiological abnormalities were found in the father, three sibs and one nephew. These findings were interpreted as the variable expression of a pleiotropic gene. The present observation and three previous familial cases of this entity strongly suggest the existence of a form of PFD determined by an autosomal dominant gene.