Petrosal cholesteatomas are rare lesions, which may be primary or acquired in nature. We report a case of primary cholesteatoma in petrous bone occurring in 51-year old woman who presented with a unilateral facial nerve palsy and conductive hearing loss, despite normal tympanic membrane appearance. Early diagnosis was facilitated by computed tomography scanning and magnetic resonance imaging. Complete cholesteatoma removal was accomplished using a transtemporal supralabyrinthine approach, which allowed hearing preservation. Facial nerve function is the main complication of these lesion. We suggest that use of CT scanning and MRI in unilateral conductive hearing loss may allow the earlier detection of the most cases of petrosal cholesteatomas.