Nephroblastoma (Wilms' tumour) is very rarely found in adult patients. We report on 10 cases to demonstrate the diagnostic and therapeutic problems. In case of flank pain, large tumour mass, fast tumour growth and young age, the possibility of Wilms' tumour should be taken into consideration even in adult patients. The chances for a successful treatment by primary surgery with adjuvant therapy are favourable for the lower stages I and II. All our patients presenting with tumour stages I and II have survived and have been free of disease for 68 months now. One of the patients with stage III Wilms' tumour died 8 months postoperatively while the other one has been free of disease for 120 months now. In the advanced stage IV no patient survived. In cases of inoperable large tumours in adults, the possibility of primary chemotherapy should be considered under certain circumstances. Rapid tumour regression may confirm the diagnosis and will make feasible a salvage operation in some cases.