ObjectiveTo study the incidence, pathogenesis, and prevention of delayed facial palsy after stapedectomy.Study DesignRetrospective case review.SettingOtology/neurotology referral center.PatientsA series of 2152 stapedectomy procedures in 2106 patients over 12 years.InterventionDelayed facial palsy after stapedectomy was studied.Main Outcome MeasureHouse-Brackmann facial nerve grading system and serum antibody titer tests for herpes simplex virus type I and type II, and varicella zoster virus.ResultsDelayed facial palsy occurred in 11 of 2152 procedures. Delayed facial palsy occurred from 5 to 16 days (mean 8) after stapedectomy. Predisposing factors were bony facial canal dehiscence with bare or bulging facial nerve herniation in 5 patients; chorda tympani nerve stretched, manipulated, or cut in 2 patients; granulomatous reaction to Gelfoam in 1 patient; fever blisters on the upper lip in 1 patient; and sinusitis in 2 patients. Elevated anti–varicella antibody titers were found in all 6 patients studied. Anti–herpes simplex type I and II antibody titers were elevated in 5 of 6 patients. Acyclovir was effective in preventing delayed facial palsy in 1 patient who had undergone revision stapedectomy and experienced delayed facial palsy after previous stapedectomy in the same ear with elevated anti–herpes antibody titer.ConclusionsDelayed facial palsy occurred in 0.51% of patients after stapedectomy. Serologic investigation suggests activation of latent herpesvirus. Mechanical irritation of the facial or chorda nerve during operation may trigger the activation. The anti-herpesvirus agent acyclovir may prevent delayed facial palsy after stapedectomy in patients suspected of having this complication.