A restrospective survey of the records of 33 patients with generalized aquired myasthenia gravis treated at Hospital das Clínicas, Medical School of The University of São Paulo, Brazil and in private practice, with and without thymectomy, is reported. Nineteen were thymectomized and 14 non operated. Both groups were demographically homogeneous and were followed from 8 to 24 years. Parameters for evaluating the natural history of disease and other ones for a comparative analysis of the improvement or remissions were established. The influence of the individualized therapy was evaluated by McNemar test (x²); the U-Mann-Whitney was used for evalution of the populational behavior groups; variable parameter with possible influence in the useful life were studied by multivariate analysis. The difference of distance between both groups was not significant: (D2= 0.08894); T2 -7.17 (Hottelling test). There were differences of the isolate clinic parameter responses in both groups, but the global analysis of the parameters did not permit to discriminate them, possibly because of interaction of the parameters influencing the analytic result. Inspite of the fact that superposition of the parameter occured when analysed for a long period, we believe the early thymectomy to be benefic. Our patients who had their operation at a younger age and specially those with recent disease had a maximum improvement.