Myasthenia gravis is caused by antibodies in the blood which attack the junctions between nerves and muscles they stimulate. Plasma exchange removes these circulating auto-antibodies. Many case series suggest that plasma exchange helps to treat myasthenia gravis. Four randomised controlled trials were identified. In the first one, of 14 participants with moderate or severe myasthenia gravis, the myasthenic muscular score after one month was not significantly different for participants treated with plasma exchange and prednisone than for those treated with prednisone alone but there can be only low statistical confidence in the results of this study because of its small size. A randomised controlled cross-over trial of only 12 participants reported the same efficacy, after four weeks, of plasma exchange or intravenous immunoglobulins for the treatment of moderate to severe myasthenia gravis, but because of bias and a very weak statistical power the data prevent any conclusion. The third, including 87 participants, showed the same efficacy, after two weeks, of plasma exchange or intravenous immunoglobulins for the treatment of myasthenia gravis exacerbation. The fourth randomised controlled trial involving 35 participants reported a benefit from plasma exchange before thymectomy but this trial was heavily biased. No trial addressed the new subtype with antibodies to a muscle specific kinase. Further research is needed to determine the value of long-term plasma exchange for treating myasthenia gravis and to compare plasma exchange with alternative short-term treatments for myasthenic crisis or before thymectomy in both types of autoimmune myasthenia.