Conclusions. High resolution CT imaging can provide useful information about the pathological exposure of the mastoid portion of the facial nerve before mastoid surgery and can assess the injury site of the facial nerve after operation. Objectives. To evaluate the diagnostic value of high resolution CT scanning of pathological exposure of the mastoid portion of facial nerve and provide valuable information for otologic surgery, and to analyse the cause of facial nerve paralysis after operation. Materials and methods. Routine CT scanning was used to examine patients with chronic suppurative otitis media and external auditory canal cholesteatoma preoperatively by axial-transverse and coronal views. If there was any pathological exposure of the mastoid portion of the facial nerve on CT imaging, then this was compared with intraoperative findings. In addition, one patient who had suffered postoperative facial nerve paralysis was also examined by CT scanning to determine whether any pre-existing pathological exposure of facial nerve could be found. Results. Through routine CT scanning six patients with chronic suppurative otitis media and three patients with external auditory canal cholesteatoma were found to have pathological exposure of the mastoid portion of the facial nerve. Coronal views could more clearly show the size and the position of the exposure; the corresponding surgical findings (pathological exposure) for the facial nerve could be confirmed in all nine patients. CT imaging could also show that the patient who had suffered postoperative facial nerve paralysis did indeed have pre-existing pathological exposure of the mastoid portion of the facial nerve.