Authors review the different theoretical and practical problems of childhood and adolescent myastenia gravis, including the heterogeneous group of congenital myasthenia and the big casuistics of the literature. There are reports on 113 cases with childhood myasthenia gravis and 96 cases of adolescent myasthenia. Ratio of these forms ranged 10.76% in childhood myasthenia and 9.14% in adolescent age, resp., 19.9% of the whole patient material. A classification is given concerning juvenile myasthenia: 1. Neonatal (transitory) myasthenia. 2. Congenital (local, non-progressive) form. 3. Congenital form with late generalized symptoms. 4. Myasthenia simulating brain-stem process. 5. Generalized childhood myasthenia. 6. Adolescent type myasthenia (juvenile form). 7. Associated myasthenia, myasthenic syndrome or reaction. A new form of the disease is described in which the congenital myasthenia changes into generalized form in the later course of the disease. Report is given on thymectomies in childhood and adolescence which produce in general excellent results. Thymic pathology and activity are dealt with.