Fibrous dysplasia typically occurs in patients between the ages of 5 and 15 years. We report the case of a middle-aged woman with longstanding monostotic fibrous dysplasia who responded well to conservative treatment. She had presented with a very long (15 yr) history of frontal headache and pressure over the frontal sinus. On examination, a protuberance was noted in the region of the right frontal sinus. No other symptoms were evident, and findings on the ENT examination were normal. Computed tomography (CT) detected a widening of the frontal bone with osteolytic changes of the cancellous bone of the diploe. Partial multiphase skeletal scintigraphy and single-photon emission CT of the cranium showed increased bone metabolism in the area of the right frontal bone. No other hot spots were seen. In view of the absence of any complications, no tissue biopsy was performed. The patient was prescribed bisphosphonates for symptom relief. Follow-up CT 1 year later revealed no progression of the lesion. Overtreatment of fibrous dysplasia should be avoided because most patients respond to conservative management. In those cases that are refractory to medical treatment, surgery--in experienced hands--can result in a good functional and cosmetic outcome.