OBJECTIVE: To determine the event-free survival (EFS) and overall survival (OS) of children with very low risk Wilms tumor (VLRWT) treated with surgery only. BACKGROUND: Previous studies suggested that postoperative chemotherapy had not improved the prognosis of children with VLRWT. A total of 77 children <24 months of age with small (<550 g) Stage I favorable histology Wilms tumors were treated with surgery only. This study was closed based on stopping rules to ensure that the 2-year EFS was > or =90%. METHODS: A total of 77 children were assessed for EFS and OS. Of these patients, 21 enrolled at the time of closure were recalled, treated with dactinomycin and vincristine (regimen EE4A), and censored for analysis thereafter. About 111 children subsequently treated with EE4A were available for comparison. RESULTS: Median follow-up of surviving patients was 8.2 years for surgery only (range, 1.9-11.8 years) and 5.2 years for the EE4A group (range, 1.6-8.9 years). The estimated 5-year EFS for surgery only was 84% (95% confidence interval [CI]: 73%, 91%); for the EE4A patients it was 97% (95% CI: 92%, 99%, P = 0.002). One death was observed in each treatment group. The estimated 5-year OS was 98% (95% CI: 87%, 99%) for surgery only and 99% (95% CI: 94%, 99%) for EE4A (P = 0.70). CONCLUSION: The surgery-only EFS was lower than anticipated but, coupled with a much higher than anticipated salvage rate of the chemotherapy naive patients whose disease recurred, led to an observed long-term OS equivalent to that seen with 2-drug chemotherapy. This approach to the treatment of patients with VLRWT eliminates the toxic side-effects of chemotherapy for a large majority of patients. A follow-up study is underway to confirm these findings.