Today the prognosis in children with nephroblastoma is excellent. With the combination of surgery, chemotherapy and radiation more than 80% of children can be cured. Because of acute toxicity and late effects of treatment (scoliosis, cardiotoxicity, fertility problems and second malignancies) a major issue in the management of children with this kind of malignancy is the reduction of chemotherapy and radiation. This is done in prospective multicenter studies. In 1989 the GPOH did join the SIOP 9 study for the treatment of Wilms' Tumors. All the SIOP studies mainly investigated the preoperative treatment. With the introduction of a centralized radiodiagnostic center in Germany (Prof. Tröger, Heidelberg) a high certainty in making the right diagnosis preoperatively without histological proof could be achieved. It could be shown in SIOP 9, that four weeks of preoperative chemotherapy with actinomycin-D and vincristine is as effective as eight weeks. 60% of patients with a localized nephroblastoma will have stage I disease at the time of surgery. The response to preoperative chemotherapy is of prognostic value. As a result of the NWTS and SIOP studies the postoperative stage and histological subtype are very important regarding prognosis. By reducing the dose of actinomycin-D to 2/3 in children under 12 kg of body weight problems with venous occlusive disease could be minimized. In the now ongoing study SIOP 93-01/GPOH postoperative treatment for patients with stage I disease and intermediate malignancy is randomized to a short and a long branch.