BACKGROUND Inflammation and oedema of the facial nerve are implicated in causing Bell's palsy. Corticosteroids have a potent anti-inflammatory action which should minimise nerve damage. OBJECTIVE The objective of this review was to assess the effect of corticosteroid therapy in Bell's palsy. METHODS We searched the Cochrane Neuromuscular Disease Group Trials Specialized Register (9 December 2008) for randomised trials, as well as MEDLINE (January 1966 to December 2008), EMBASE (January 1980 to December 2008) and LILACS (9 December 2008). We contacted known experts in the field to identify additional published or unpublished trials. METHODS Randomised trials comparing different routes of administration and dosage schemes of corticosteroid or adrenocorticotrophic hormone therapy versus a control group where no therapy considered effective for this condition was administered, unless it was also given in a similar way to the experimental group. METHODS Two authors independently assessed eligibility, trial quality, and extracted the data. RESULTS Eight trials with a total of 1569 participants were included. Allocation concealment was appropriate in six trials, and the data reported allowed an intention-to-treat analysis in four, while unpublished data from the fifth and sixth trials were provided by the authors. The data included in the main outcome of this meta-analysis were collected from seven trials with a total of 1507 participants. Overall 175/754 (23%) of the participants allocated to corticosteroids had incomplete recovery of facial motor function six months or more after randomisation, significantly less than 245/753 (33%) in the control group (risk ratio (RR) 0.71, 95% confidence interval (CI) 0.61 to 0.83). There was, also, a significant reduction in motor synkinesis during follow-up in those receiving corticosteroids (RR 0.6, 95% CI 0.44 to 0.81). The reduction in the proportion of patients with cosmetically disabling sequelae six months after randomisation, however, was not significant (RR 0.97, 95% CI 0.44 to 2.15). The trial not included in the primary outcome of this meta-analysis showed a non-significant difference in outcomes between the arms. CONCLUSIONS The available evidence from randomised controlled trials shows significant benefit from treating Bell's palsy with corticosteroids.