Objectives:The purpose of this report is to provide data on the incidence of delayed facial palsy (DFP) after tympanomastoid surgery, compare incidence among various otologic and neurotologic procedures, and discuss the possible etiology.Study Design:The study design was a retrospective case review.Setting:The study was conducted at a tertiary referral center.Patients:The records of 486 patients with normal facial function before tympanomastoid surgery were reviewed.Intervention:Patients underwent tympanomastoid surgery.Outcome Measures:Delayed facial palsy was defined as facial palsy occurring more than 72 hours after surgery.Results:Seven of 486 (1.4%) patients had DFP after tympanomastoid surgery. In two patients, the DFP was caused by a postoperative wound infection. Facial palsy in the other five patients likely was caused by viral reactivation.Conclusions:Published data for otologic surgery suggest a rising incidence of DFP with increased manipulation of the sensory branches of the facial nerve. Viral reactivation is postulated to be an important contributing mechanism in the development of DFP. A number of viruses could potentially cause this phenomenon, but observations in this study implicate the varicella zoster virus. Patients with a history of viral reactivation may be at greater risk for development of this complication.