BACKGROUND/PURPOSE: Cystic partially differentiated nephroblastoma (CPDN) is a rare variant of Wilms' tumor thought to be more favorable than standard nephroblastoma. The purpose of this report is to examine the outcome of children with CPDN, after nephrectomy, treated with vincristine and dactinomycin based chemotherapy (+/- doxorubicin) or no chemotherapy. METHODS: Patients were registered with the National Wilms' Tumor Study Group (NWTSG) and data were collected prospectively. All patients had central review by the NWTSG Pathology Center to confirm the diagnosis of CPDN. RESULTS: Twenty-one patients were identified with a diagnosis of CPDN. Thirteen patients received chemotherapy, and 8 patients did not. In the chemotherapy group the stage distribution was as follows: stage I (n = 10), stage II (n = 2), stage V (n = 1). In the no-chemotherapy group, all 8 patients were stage I. All patients had complete tumor resection. There were no cases of disease progression or recurrence in any patient. In patients receiving chemotherapy, 30% (n = 4) had toxicities causing dose reduction. CONCLUSIONS: The outcome of patients with CPDN is favorable with 100% survival rate and no recurrences. For stage I patients, treatment with complete tumor resection appears to be as efficacious as nephrectomy plus chemotherapy. Stage II patients also have excellent outcome when treated with tumor resection and postoperative vincristine and dactinomycin.