[en] The experience of a large Cancer Institute in treating invasive thymoma has been reviewed. Twenty-eight patients received radiotherapy following biopsy or incomplete resection of thymoma. The overall survival was 53 percent at 5 years and 44 percent at 10 years. Treatment was generally well tolerated but 3 patients (11 percent) developed significant side effects from the radiotherapy and two of these died. Radiotherapy appeared to be more effective in patients who had a small volume of residual disease after surgery. An attempt was made to identify prognostic factors but none reached statistical significance. The radiation dose, field size and the use of systemic treatment are discussed. (author). 26 refs.; 2 figs.; 3 tabs