BACKGROUND Antiviral agents against herpes simplex virus are widely used in the treatment of idiopathic facial paralysis (Bell's palsy), but their effectiveness is uncertain. Significant morbidity can be associated with severe cases. OBJECTIVE This review addresses the effect of antiviral therapy on Bell's palsy. METHODS We updated the search of the Cochrane Neuromuscular Disease Group Trials Register (December 2008), MEDLINE (from January 1966 to December 8 2008), EMBASE (from January 1980 to December 8 2008) and LILACS (from January 1982 to December 2008). METHODS Randomized trials of antivirals with and without corticosteroids versus control therapies for the treatment of Bell's palsy. METHODS Twenty-three papers were selected for consideration. RESULTS Seven trials including 1987 participants met the inclusion criteria, adding five studies to the two in the previous review.Incomplete recovery at one year. There was no significant benefit in the rate of incomplete recovery from antivirals compared with placebo (n = 1886, RR 0.88, 95% CI 0.65 to 1.18). In meta-analyses with some unexplained heterogeneity, the outcome with antivirals was significantly worse than with corticosteroids (n = 768, RR 2.82, 95% CI 1.09 to 7.32) and the outcome with antivirals plus corticosteroids was significantly better than with placebo (n = 658, RR 0.56, 95% CI 0.41 to 0.76).Motor synkinesis or crocodile tears at one year. In single trials, there was no significant difference in long term sequelae comparing antivirals and corticosteroids with corticosteroids alone (n = 99, RR 0.39, 95% CI 0.14 to 1.07) or antivirals with corticosteroids (n = 101, RR 1.03, 95% CI 0.51 to 2.07).Adverse events.There was no significant difference in rates of adverse events between antivirals and placebo (n = 1544, RR 1.06, 95% CI 0.81 to 1.38), between antivirals and corticosteroids (n = 667, RR 0.96, 95% CI 0.65 to 1.41) or between the antiviral-corticosteroid combination and placebo (n = 658, RR 1.15, 95% CI 0.79 to 1.66). CONCLUSIONS High quality evidence showed no significant benefit from anti-herpes simplex antivirals compared with placebo in producing complete recovery from Bell's palsy. Moderate quality evidence showed that antivirals were significantly less likely than corticosteroids to produce complete recovery.