Data on delayed facial nerve palsy (DFNP) following endolymphatic sac enhancement surgery are limited. We conducted a retrospective chart review to determine the incidence, possible predisposing factors, treatment, and prognosis of DFNP in such cases. We reviewed the records of 779 patients who had undergone endolymphatic sac surgery for intractable Ménière disease from January 1997 through December 2007 at a tertiary care otologic referral center. We found 5 cases (0.64%) of postoperative DFNP. The length of time between surgery and the onset of DFNP ranged from 7 to 20 days (mean: 11). Paralysis was incomplete in all 5 patients. Four of these patients had an abnormal mastoid bone anatomy, as the sigmoid sinus was either anteriorly or anteromedially displaced. The 5 patients had been treated with a steroid, either with or without an antiviral, and all 5 experienced a complete recovery of facial nerve function within 8 weeks of the onset of their paralysis. It is difficult to delineate the exact etiology of DFNP following endolymphatic sac surgery, but we speculate that factors such as physical injury to the nerve and/or a viral reactivation might have played a role. Also, the unusual mastoid bone anatomy seen in 4 of these patients might have been responsible, as well.