Delayed onset facial nerve dysfunction following acoustic neuroma surgery is an under-appreciated phenomenon. The authors have recently reviewed long-term (> 1 year) facial nerve outcome in 129 patients who underwent acoustic neuroma removal with the aid of cranial nerve monitoring between 1986 and 1990. The facial nerve was anatomically preserved in 99.2% of the patients, and at one year, 90% of all the patients had House-Brackmann (H-B) grade I or II facial nerve function. Delayed onset worsening of facial nerve function was noted in 38 of 129 (29%) patients, most of which occurred in the first few postoperative days. The incidence increases to 41% (38 of 93) when corrected for those with immediate H-B grade VI weakness, and who therefore could not manifest further deterioration. The facial nerve function either deteriorated from normal to abnormal or increased in severity of weakness. Delayed facial palsy was not related to the size of tumor or the surgical approach. The most common occurrence was that of a patient with H-B grade I or II facial nerve function worsening to H-B grade VI in the postoperative period. The prognosis for recovery of facial nerve function following delayed palsy was excellent. In the majority of cases, the recovery was complete within the first 6 months without specific treatment. Comparable to the patients without delayed palsies, 89% (34 of 38) of the cases had H-B grade I or II and 97% (37 of 38) had H-B grade III or better facial nerve function at 1 year. This review suggests a surprisingly high incidence of delayed facial palsy following acoustic neuroma surgery, which fortunately has an excellent prognosis for spontaneous recovery.