The results of thymectomy in the treatment of myasthenia gravis (MG) are reviewed in the light of a personal series of 662 MG patients, operated upon during the last 15 years. In 500 MG patients without thymoma, the following results have been achieved: remission 37.9%, improvement 49.4%, unchanged or worse 7.4%, dead 5.2%. There is no sex prevalence and the remission rate is higher in patients under 40 years of age (P less than 0.01), with mild disease (P less than 0.05), with a MG duration of less than 1 year (P less than 0.05) and with a follow-up length of between 5 and 10 years (P less than 0.01). No correlations are found between outcome and thymic histology. The results of 162 MG patients with thymoma are: remission rate 15.7%, improvement 60.3%, unchanged or worse 3.7% and dead 20.1%. The remission rate is higher with mild symptoms (P less than 0.05) and when the tumour is encapsulated (P less than 0.02). The postoperative mortality is 0.8% (none in the last 5 years) for non-thymomatous MG and 4.9% for thymomatous MG (2 of 8 patients died of pancytopaenia and 1 of pulmonary embolism).