Fibrous dysplasia is an uncommon benign disorder of unknown etiology. It represents a disturbance of normal bone development--specifically a defect in osteoblastic differentiation and maturation that originates in the mesenchymal precursor of the bone. Because fibrous dysplasia shows a predilection for the facial and cranial bones, where it causes deformity and dysfunction, the disease is of particular interest to the otolaryngologist. In this paper, we report a case of fibrous dysplasia of the temporal bone, the first symptom of which was a mixed hearing loss. We discuss the characteristic features of this specific location of the disease, the differential diagnosis, and the treatment policy. We also address the issue of secondary sensorineural hearing loss.