Between 1980 and 1988, in a prospective study of 373 children with Wilms' tumour throughout the Federal Republic of Germany, the results of various pre- and postoperative treatment schedules were analysed. There were 184 boys and 189 girls, mean age 3 11/12 (0-27) years. One third each was in group I, II or III-V, respectively. In 52% of cases the tumour volume, measured by ultrasound, was more than 400 ml. 218 of the children were called protocol patients, the remaining 155 served as observation patients, because the latter had histological variants or there had been marked treatment deviations. The stage-adapted treatment always included operation, in 30% of children after pre-operative chemo- or radiotherapy. Radiotherapy was given in selected patients in stage II and always to those in stages III, IV or V. Chemotherapy consisted of Actinomycin D and vincristine, adriamycin was added for stages III-V and cyclophosphamide or ifosfamide for histologically highly malignant variants. Of the 218 protocol patients 196 (90%) were alive without recurrence, after a mean observation time of more than 7 years. Radiotherapy was given to only 105 of the 218 protocol patients. The prognosis of the 155 observation patients differed according to the histology: those with clear-cell type had a better prognosis than previously reported. Among the total group of 373 patients 305 (81.8%) have remained without recurrence after more than 6 years.