Wilms tumor is the most common primary malignant renal tumor of childhood, representing about six percent of all childhood cancers in the United States. Developments in surgery, radiation therapy, and chemotherapy have led to a dramatic change in the prognosis for most patients, and Wilms tumor has become a paradigm for multimodal treatment of a pediatric malignant solid tumor. The authors review the progress made in the diagnosis and management of children with Wilms tumor.