Fibrous dysplasia is an uncommon benign disorder of unknown aetiology. It most likely represents a disorder of normal bone development. As it may occasionally involve the temporal bone, and encroach on the middle cranial fossa, it is of interest to the neurosurgeon. Fibrous dysplasia of the cystic variety is very uncommon. We report a case of a large cystic fibrous dysplasia involving predominantly the squamous temporal bone. The radiology and histology are discussed, and its differentiation from other lesions.