Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction caused by auto-antibodies. MG is characterized by weakness in skeletal muscles and occurs in all ages, but mostly among young adult women and in people of both sexes over the age of 60 years. The disease has a wide variation in severity, where in milder cases only symptom-relieving choline esterase blockers may be sufficient. In many cases, however, immunomodulatory drugs are required. Traditionally MG has been treated with high doses of corticosteroids over longer time periods, which causes significant risks of side effects. Therefore, since several decades, oral immunosuppressive drugs have been used in order to reduce the need for steroids. This group includes azathioprine, cyclosporine and mycophenolate. However, none of these drugs has been approved for use in MG and the effect is usually delayed. There is thus a great need to develop newer treatment algorithms for MG, for example including more effective biological drugs. Several small observational studies have shown that rituximab, an anti-CD20 monoclonal antibody that eliminate B cells, can have good effects in treatment refractory MG. The aim of the present study is to study the effect of rituximab compared to placebo in the treatment of new onset MG of moderate to severe symptomatology.