The records of all patients treated for thymoma in the Department of Radiotherapy of the University of Torino between 1970 and 1988 were reviewed. There were 77 patients in stage III or IVa (59 in stage III and 18 in stage IVa); 74 patients were operated upon before radiotherapy and 3 had a pre-operative irradiation followed by surgery and post-operative boost. Complete resection was possible in 55.9% of cases with stage III and in none with stage IVa. Subtotal resection was done in 35.6% of patients in stage III and 83.3% in stage IVa. 8 patients had only a biopsy: 5 in stage III (8.5%) and 3 in stage IVa (16.6%). Post-operative radiation doses ranged between 39.6 and 46 Gy to the whole mediastinum followed by a 10-16 Gy boost on smaller fields in cases presenting residual disease after surgery. The pre-operative dose was 30 Gy followed by a post-operative boost of 16-24 Gy. Conventional fraction sizes of 1.8-2 Gy were always used. The 10 years survival rate was 58.3%. There was a significant difference between stage III (70.9%) and stage IVa (26.3%) (p less than 0.0004). Survival of patients in stage III was not significantly affected by the type of surgery. No significant difference in survival or recurrence rate was observed in patients with different histologies and in patients with or without myasthenia. Thoracic relapses occurred in 15.2% of patients in stage III and in 50% of patients in stage IVa (p less than 0.01). Only 7 relapses (9.1%) were within the limits of the radiation field.(ABSTRACT TRUNCATED AT 250 WORDS)