Wilms tumor (WT), or nephroblastoma, is the most common primary malignant renal tumor of childhood. It is the second most common solid organ abdominal tumor encountered in childhood, accounting for 6% of all pediatric tumors. The annual incidence is 8.1 per million children. This results in 600–700 new cases each year in North America. Outcomes for children with WT have improved dramatically over the last 50 years, with long-term survival in both North America and European trials approaching 85%. Moreover, many of the low-stage tumors have survival rates between 95 and 99%. The treatment strategy for children with WT has also evolved. It is currently based on traditional risk factors, such as stage and histology, as well as genetic markers, response to therapy and consideration of the risk of late effects. The goal of “risk-based management” is to maintain excellent outcomes but to spare children with low-risk tumors the long-term side effects of intensive chemo- and radiation therapy and to use more intense therapy for high-risk tumors to minimize recurrence rates (Table 92.1). Risk-based therapy requires a multidisciplinary team that includes oncologists, radiologists, surgeons, radiation oncologists, pathologists, social workers and nurses. Surgeons play a critical role in diagnosis, staging and treatment, and their technical skill and judgment have a direct impact on therapeutic decision-making and patient outcome. The current outcome data for children with WT from the National Wilms Tumor Study are shown in Table 92.2.