Guillain-Barré syndrome (GBS) is an acute paralysing disease caused by inflammation of the peripheral nerves, which corticosteroids would be expected to benefit. To examine the ability of corticosteroids to hasten recovery and reduce the long-term morbidity from GBS. We searched The Cochrane Neuromuscular Disease Group Specialized Register (1 November 2011), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 4), CENTRAL (2011, Issue 4), MEDLINE (January 1966 to October 2011) and EMBASE (January 1980 to October 2011). We included randomised controlled trials (RCTs) or quasi-RCTs of any form of corticosteroid or adrenocorticotrophic hormone in GBS. Our primary outcome was change in disability grade on a seven-point scale after four weeks. Secondary outcomes included time from randomisation until recovery of unaided walking, time from randomisation until discontinuation of ventilation (for those ventilated), death, death or disability (inability to walk without aid) after 12 months, relapse, and adverse events. Two authors extracted the data independently. No new trials were discovered in the new searches in June 2009 or November 2011. Six trials with 587 participants provided data for the primary outcome. According to moderate quality evidence, the disability grade change after four weeks in the corticosteroid groups was not significantly different from that in the control groups, mean difference (MD) 0.36 less improvement (95% confidence intervals (CI) 0.16 more to 0.88 less improvement). In four trials of oral corticosteroids with 120 participants in total, there was significantly less improvement after four weeks with corticosteroids than without corticosteroids, MD 0.82 disability grades less improvement (95% CI 0.17 to 1.47). In two trials with a combined total of 467 participants, there was no significant difference, MD 0.17 (95% CI -0.06 to 0.39) of a disability grade more improvement after four weeks with intravenous corticosteroids. According to moderate to high quality evidence, there were no significant differences between the corticosteroid-treated and the control groups in any of the secondary efficacy outcomes. Diabetes was significantly more common and hypertension significantly much less common in the corticosteroid-treated participants. According to moderate quality evidence, corticosteroids given alone do not significantly hasten recovery from GBS or affect the long-term outcome. According to low quality evidence oral corticosteroids delay recovery. Diabetes requiring insulin was significantly more common and hypertension less common with corticosteroids.