Myasthenia gravis (MG) is a heterogeneous disease composed of several entities with disturbed neuromuscular transmission. The most frequent and clinically most important form of MG is an acquired autoimmune MG which includes more than 90% of all patients with failure of neuromuscular transmission. The main clinical feature of MG is changeable pathologic fatigability and weakness of one or more skeletal muscles and variable distribution of affected muscles. The disease is characterized by relapses and remissions. In 15% of patients the symptoms are limited to extraocular muscles causing variable ptosis, squint and double vision (Ocular MG). In remaining 85% of patients, during the first three years, the disease involves the majority of the head, neck and extremity skeletal muscles (Generalized MG). The clinical diagnosis may be sufficiently established by typical history, present or induced neurological signs of changeable muscle weakness and positive pharmacological tests. The assessment of the severity of the disease as well as the assessment of working capability is performed according to the classification recommended by Myasthenia Gravis Foundation of America (MGFA). The standardized score of the disease severity is based on testing function and strength of 9 groups of skeletal muscles. At the onset of the disease, regardless of the clinical form, the patient is incapable of work and subjected to hospitalization, clinical investigation and treatment. The efficacy of anticholinesterase drugs, thymectomy and/or immunosuppression determines the working capability and is recommended to be assessed six months after the initiation of treatment procedure.