Introduction: Wilms tumor (WT) is the most common form of malignant kidney tumor in childhood. According to PINDA protocols, its treatment includes, depending on stage and presentation, early surgery, radiotherapy (RT) and chemotherapy (CT). The objective of this work is to review the results of all patients of the National Cancer Institute (NCI) with this condition. Patients and Method: A retrospective review of all patients diagnosed with WT at the NCI was conducted. Patient population, RT treatment received and overall survival results were described and prognostic factors were searched. Results: From September 1993 to December 2010, 110 children were treated with RT. The median age at diagnosis was 3.6 years old. Median follow-up was 128 months after RT. In June 2012, out of a total of 107 patients with follow up, 22 had died, 19 due to disease progression. All deaths occurred within three years of treatment. Overall survival at 2, 4 and 12 years old was 82 %, 78 %, 78 % respectively. A multivariate analysis showed that each day after surgery and without starting RT, the chances of survival decreased (p = 0.04). Conclusions: WT treatment has an excellent prognosis. Survival after 3 years stabilizes without presenting complications, regardless of the group to which the patient belongs. Among the prognostic factors for patients with RT prescription, this radiation should be started early, as close to the surgery as possible.