Cemento-ossifying fibromas are benign lesions of the jaw, which arise from the periodontal membrane. Histopathologically these are composed of fibrous tissues with calcified structures resembling bone and cementum. Surgical resection is the treatment of choice. They have rarely been reported in the ethmoid sinus, maxillary sinus and sphenoid sinus Mastoid bone is an extremely rare site of such tumors. Only one case of cemento-ossifying fibroma of petromastoid bone has been reported before. We present a case of cementoossifying fibroma involving the petromastoid bone, with the large intracranial component causing compression on the cerebellum. This unique case may provide insight into the etiopathogenesis of these tumors.