Objective: To establish the frequency of occurrence of delayed facial nerve paralysis following tympano-mastoid surgery in our department and to determine the aetiological factors and long term prognosis.

Setting: Tertiary care academic centre.

Materials and methods: A retrospective review of all patients who had undergone tympano-mastoid surgery in our department over the previous five years was carried out. A total of 219 patients were included in the study. Only two patients were identified as having delayed onset facial nerve palsy over this period of time. The patients' medical records were reviewed and the patients clinically assessed.

Results: The frequency of delayed onset facial nerve palsy following tympano-mastoid surgery in our series was 0.91 per cent. Facial weakness set in on day eight and day 14 in the two patients. Serological investigations in both patients revealed raised titres of immunoglobulin (Ig) M and IgG to varicella-zoster virus, confirming the presence of varicella-zoster infection. In our experience, the combined use of prednisone and acyclovir was an effective form of treatment for both patients, whose facial nerve function fully recovered within six months of onset.

Conclusion: The incidence of delayed facial nerve palsy following tympano-mastoid surgery is low. It can occur up to two weeks after the surgery. Our two cases confirm viral reactivation to be an important aetiological factor in the development of delayed onset facial nerve palsy. The overall prognosis for delayed facial nerve palsy following tympano-mastoid surgery appears to be good.