The role of thymectomy in the management of myasthenia gravis is reviewed in the light of the published data and of a personal series. The patients in whom the operation is most successful are non thymomatous patients aged between 10 and 40 years with an MG history of less than 3 years. There is no sex prevalence. Lasting improvement may be expected. There are no proven correlations between biological indices like the germinal centers in the thymus and/or AChR antibody titers and the postoperative course of the disease. Complete removal of the thymus seems to be crucial and hence the transsternal approach is preferred. The operation, less effective in patients with thymoma than in those with an active thymus, is nonetheless necessary to in these patients prevent putative damage to surrounding organs from thymoma infiltration. Why thymectomy should be effective in patients with an active thymus and not in those with a thymoma may be revealed by in vitro studies of the interactions between thymic cells and peripheral B cells, now in progress.