Forty operated cases of myasthenia gravis correspond to 14 thymomas, 18 hyperplasias and 8 vestigial thymus : 3 stages, I, 28 stages, II, 6 stages III, 3 stages IV. For vestigial thymus and moderate hyperplasias, cervicotomy was used in 11 cases. Surgery allowed 15 remissions, 12 ameliorations, 11 failures, aggravations and late deaths, and 2 post-operative deaths (one of them avoidable). Apart from its oncologic interest in thymomas (1/3 of the patients), thymectomy is beneficial in 2/3 of the cases of myasthenia gravis in general.