Microscopic structure and immunologic function of the thymus gland are outlined, with an emphasis on its role in the process of T and B lymphocytes maturation. Other types of thymic cells are also described, including epithelial and myoid cells that presumably have a central role in initiation of an autoimmunologic process leading to myasthenic symptoms development. A detailed account is presented of issues concerning pathophysiology of myasthenia, the structure of nicotinic acetylcholine receptor (AchR) at neuromuscular junctions, and mechanisms underlying its destruction by autoantibodies. The role of T and B lymphocytes, of various cytokine types, of autoantibodies to various striated muscle antigens, as well as a possible role of genetic and bacterial factors in the development of myasthenia gravis are discussed. In conclusion it is stressed that since recent research findings go beyond the classic theory of myasthenia, a new consistent theory of the disease immunopathogenesis must be created in the future to place all the newly discovered phenomena in a logical conceptual structure.