BACKGROUND Myasthenia gravis is an autoimmune disease in which autoantibodies interfere with neuromuscular transmission. As with other autoimmune diseases, people with myasthenia gravis would be expected to benefit from intravenous immunoglobulin. OBJECTIVE The objective of this review was to examine the efficacy of intravenous immunoglobulin for treating exacerbations of myasthenia gravis or for chronic myasthenia gravis. METHODS We searched the Cochrane Neuromuscular Disease Group trials register (March 2005) and MEDLINE (January 1966 to March 2005) using 'myasthenia gravis' and 'intravenous immunoglobulin' as the search terms. METHODS We included all randomised or quasi-randomised trials in which intravenous immunoglobulin was compared with no treatment, placebo or plasma exchange, in people with myasthenia gravis. METHODS One author extracted the data and the two others checked these data and the source from which they were derived. For methodological reasons, no formal meta-analysis was performed. RESULTS We identified five randomised controlled trials, all of which investigated short-term benefit. The first study of 87 participants with exacerbation found no statistically significant difference between immunoglobulin and plasma exchange after two weeks. The second study of 12 participants with moderate or severe myasthenia gravis treated in a crossover design trial found no statistically significant difference in the efficacy of immunoglobulin and plasma exchange after four weeks. The third study with 15 participants with mild or moderate myasthenia gravis found no statistically significant difference in efficacy of intravenous immunoglobulin and placebo after six weeks. The fourth study terminated early. It included 33 participants with moderate exacerbations of myasthenia gravis and showed no statistically significant difference in the efficacy of intravenous immunoglobulin and methylprednisolone. The fifth trial including 173 people with myasthenia gravis exacerbations, showed no superiority of intravenous immunoglobulin 1 g/kg on two consecutive days over intravenous immunoglobulin 1 g/kg on a single day. CONCLUSIONS In severe exacerbations of myasthenia gravis, one randomised controlled trial did not show a significant difference between intravenous immunoglobulin and plasma exchange. Another showed no significant difference in efficacy between 1 g/kg and 2 g/kg of intravenous immunoglobulin. A further trial showed no significant difference between intravenous immunoglobulin and oral methylprednisolone. In chronic myasthenia gravis, there is insufficient evidence from randomised trials to determine whether intravenous immunoglobulin is efficacious. More research is needed to determine whether intravenous immunoglobulin reduces the need for steroids as suggested by two case series.