Idiopathic (Bell's) facial palsy is a self-limiting, non-life threatening, and spontaneously remitting disorder. The natural history of Bell's palsy is favorable: 84% of 1011 patients with Bell's palsy studied by one investigator recovered satisfactorily without treatment, and no valid clinical trials conducted to date have provided definitive evidence that treatment with steroids or surgery improves upon this figure. The authors studied 273 patients with Bell's palsy to evaluate the prognostic significance of evoked eleetromyography in predicting the possible benefit of transmastoid facial nerve surgical decompression. The results indicated that even when evoked electromyography was used to select those patients who might benefit most from transmastoid surgery, outcome in patients treated surgically was no better than can be expected to occur without treatment. Based upon these observations, transmastoid facial nerve surgery is not recommended to treat Bell's palsy because no benefits have been identified which outweigh the risks of surgery.