Wilms tumor, although rare, is the most frequent malignant renal tumor in children. With approximately 70 new cases diagnosed annually in Italy, it is important to collect these rare cases and to treat them in a uniform way. At the dawn of this century virtually all children with Wilms tumors died: today 95% of them survive; the treatment is carefully tailored to well defined risk factors (histology-stage-molecular markers) to minimize short and long-term toxicities. The object of this review is to describe the pathway to the progress. The most important step was to recognize that a single institution could not collect enough patients to answer complex questions, whereas this was possible for super-groups like the National Wilms Tumor Study Group (NWTSG) in the USA, the multinational SIOP study group in Europe, the United Kingdom group, the Italian group (CNR-AIEOP) and more recently the Brazilian one. Wilms tumor is the paradigm for the multimodal treatment of a pediatric malignant solid tumor, the development in surgical technique, the recognition of the sensitivity of Wilms tumor to irradiation and the availability of several chemotherapeutic agents led to a dramatic change in the prognosis for most patients. Much progress has been made in the study of histopatology of childhood renal tumors: the patients must be stratified into two groups, the favourable and the unfavourable histology, further subdivided into anaplasic tumors (focal or diffuse), clear cell tumors and rhabdoid tumors. The past few years have provided a breakthrough in understanding some of the genetic factors involved in Wilms' tumor: moreover, possible chromosomal prognostic factors have been identified: loss of heterozygosity of 16q markers and 1p markers. Today the results of the treatment of Wilms tumors are very good. In the NWTS-3 the four year relapse-free survival rate in stage 1 with favourable and with anaplastic histology was 92%, in stage 2 with favourable histology 88%, in stage 3 with favourable histology 79%, in stage 4 and in stage 2, 3 and 4 with unfavourable histology 71%. The Italian group has obtained less impressive results in the ¿80, but similar results in the first stage with the ¿92 protocol. There is a debate about the immediate nephrectomy preferred by NWTS and the preoperative strategies adopted by SIOP group. Successful treatment may be associated with many late effect: in patients cured of Wilms tumor the risk of congestive heart failure has been less than 1.7%, the risk of a second tumor less than 1%. The must important late effect remains the relapse of the disease: the risk is about 14-20%.