OBJECTIVE This article reviews the clinical presentations, diagnostic findings, and treatment options for autoimmune myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome. RESULTS Immunologic research is unraveling the immunopathology of MG and identifying targets for novel immune-based therapy of this condition. MG patients with antibodies to muscle-specific tyrosine kinase (MuSK) frequently present with symptoms and clinical findings that suggest nerve or muscle disease. CONCLUSIONS Early diagnosis and treatment have a marked effect on outcome in these diseases. In most cases, the diagnosis of MG or Lambert-Eaton myasthenic syndrome can be made from the history, supplemented with directed questions, and a physical examination designed to demonstrate variable weakness in affected muscle groups. Appropriate confirmatory tests almost always establish the diagnosis. Although several novel treatment modalities for MG are under investigation, currently available therapies produce substantial improvement in function and quality of life in most patients with this condition. Knowledge about the dosing, adverse effects, and costs of immunomodulatory therapies is essential for the effective management of patients with MG and Lambert-Eaton myasthenic syndrome.