In the years 1979-1982, 83 patients with malignant teratoma of the testis who had retroperitoneal adenopathy at presentation or after a period of surveillance were treated. Complete radiological resolution of disease was obtained in 34 patients and a residual mass remained in 26, the remainder having progression of the para-aortic or other metastatic disease. There was no para-aortic relapse in 47 patients receiving radiotherapy post-chemotherapy whereas 2/11 who did not receive radiotherapy or an immediate retroperitoneal node dissection relapsed. Morbidity from radiotherapy was minimal apart from subcutaneous fibrosis in the irradiated area of 6 patients. It is concluded that radiotherapy is effective in sterilising minimal residual tumour post-chemotherapy and may be considered as an alternative to surgery.