The authors have treated 42 patients with thymoma and report on their experience. The mode of discovery, and notably the thymoma-myasthenia association in 8 cases (20%), the diagnostic approach and the management of the disease--surgery alone : 18 cases, surgery combined with radiotherapy : 24 cases and/or with chemotherapy : 5 cases--were analyzed. The thymomas were classified according to the G.E.T.T. system after re-examination of the histological sections. The course of the disease was studied. The overall survival rate, which depends on tumoral stage, was 71% at 4 years and 69% at 10 years; 5 patients died of the disease and 9 of other causes, including 5 who presented with a blood disease. This series is compared with other published series. The frequency of myasthenia and the respective prognostic values of anatomico-surgical, histological and histo-immunological classifications are discussed.