The clinical history and neurological examination provide the most important data on which the diagnosis of autoimmune myasthenia gravis (MG) is based. MG produces symptomatic weakness that predominates in certain muscle groups and typically fluctuates in response to effort and rest. The diagnosis of MG therefore depends on the recognition of this distinctive pattern of fatigable weakness. Laboratory confirmation of the clinical diagnosis may be obtained using pharmacological, electrophysiological, and serological (immunological) tests. This article reviews the tests used to confirm the diagnosis of MG.