Aim: To standardize diagnosis and treatment of childhood Wilms tumor (WT) in Turkey. Methods and patients: Between 1998 and 2006, WT patients were registered from 19 centers. Patients <16 years with unilateral WT whose treatment started in first postoperative 3 weeks were included. Treatments were stage I favorable (FH) and unfavorable histology (UH) patients, VCR + Act-D; stage IIA FH, VCR + Act-D; stage IIB FH, VCR + Act-D + radiotherapy (RT); stage III-IV FH, VCR + Act-D + adriamycin (ADR) + RT; stages II-IV UH tumors, VCR + Act-D + ADR + etoposide + RT. Results: 165/254 registered cases were eligible (bilateral, 5.9%) [median age 3.0 years; M/F: 0.99; 50/165 cases <= 2 years]. 9.7% cases had UH tumors. Disease stages were stage I 23.6%; IIA 36.4%; IIB 5.5%; III 22.4%; IV 12.1%. Cases >2 years had significantly more advanced disease. 1/11 cases with recurrent disease died; 2/165 had progressive disease, 2/165 had secondary cancers, and all 4 died. In all cases 4-year OS and EFS were 92.8 and 86.5%, respectively. Both OS and EFS were significantly worse in stage IV. Conclusions: Despite problems in patient management and follow-up, treatment results were encouraging in this first national experience with a multicentric study in pediatric oncology. Revisions and modifications are planned to further improve results and minimize short- and long-term side effects.