Background: Guillain-Barré syndrome (GBS) is an acute, paralysing, inflammatory peripheral nerve disease. Intravenous immunoglobulin (IVIg) is beneficial in other autoimmune diseases. This is an update of a review first published in 2001 and previously updated in 2003, 2005, 2007, 2010 and 2012. Other Cochrane systematic reviews have shown that plasma exchange (PE) significantly hastens recovery in GBS compared with supportive treatment alone, and that corticosteroids alone are ineffective., Objectives: We had the following four objectives.1. To examine the efficacy of intravenous immunoglobulin (IVIg) in hastening recovery and reducing the long-term morbidity from Guillain-Barré syndrome (GBS).2. To determine the most efficacious dose of IVIg in hastening recovery and reducing the long-term morbidity from GBS.3. To compare the efficacy of IVIg and plasma exchange (PE) or immunoabsorption in hastening recovery and reducing the long-term morbidity from GBS.4. To compare the efficacy of IVIg added to PE with PE alone in hastening recovery and reducing the long-term morbidity from GBS., Search Methods: We searched the Cochrane Neuromuscular Disease Group Specialized Register (2 December 2013), CENTRAL (2013, Issue 12 in The Cochrane Library), MEDLINE (January 1966 to November 2013) and EMBASE (January 1980 to November 2013). We checked the bibliographies in reports of the randomised trials and contacted the authors and other experts in the field to identify additional published or unpublished data., Selection Criteria: Randomised and quasi-randomised trials of IVIg compared with no treatment, placebo treatment, PE, or other immunomodulatory treatments in children and adults with GBS of all degrees of severity. We also included trials in which IVIg was added to another treatment., Data Collection and Analysis: Two authors independently selected papers, extracted data and assessed quality. We collected data about adverse events from the included trials., Main Results: Twelve trials were found to be eligible for inclusion in this review. Seven trials with a variable risk of bias compared IVIg with PE in 623 severely affected participants. In five trials with 536 participants for whom the outcome was available, the mean difference (MD) of change in a seven-grade disability scale after four weeks was not significantly different between the two treatments: MD of 0.02 of a grade more improvement in the intravenous immunoglobulin than the plasma exchange group; 95% confidence interval (CI) 0.25 to -0.20. There were also no statistically significant differences in the other measures considered. Three studies including a total of 75 children suggested that IVIg significantly hastens recovery compared with supportive care. The primary outcome for this review, available for only one trial with 21 mildly affected children, showed significantly more improvement in disability grade after four weeks with IVIg than supportive treatment alone, MD 1.42, 95% CI 2.57 to 0.27.In one trial involving 249 participants comparing PE followed by IVIg with PE alone, the mean grade improvement was 0.2 (95% CI -0.14 to 0.54) more in the combined treatment group than in the PE alone group; not clinically significantly different, but not excluding the possibility of significant extra benefit. Another trial with 34 participants comparing immunoabsorption followed by IVIg with immunoabsorption alone did not reveal significant extra benefit from the combined treatment.Adverse events were not significantly more frequent with either treatment, but IVIg is significantly much more likely to be completed than PE.Small trials in children showed a trend towards more improvement with high-dose compared with low-dose IVIg, and no significant difference when the standard dose was given over two days rather than five days., Authors' Conclusions: A previous Cochrane review has shown that PE hastens recovery compared with supportive treatment alone. There are no adequate comparisons of IVIg with placebo in adults, but this review provides moderate quality evidence that, in severe disease, IVIg started within two weeks from onset hastens recovery as much as PE. Adverse events were not significantly more frequent with either treatment but IVIg is significantly much more likely to be completed than PE. Also, according to moderate quality evidence, giving IVIg after PE did not confer significant extra benefit. In children, according to low quality evidence, IVIg probably hastens recovery compared with supportive care alone. More research is needed in mild disease and in patients whose treatment starts more than two weeks after onset. Dose-ranging studies are also needed and one is in progress.