Background Completely necrotic Wilms tumor (CN‐WT) following preoperative chemotherapy has been regarded as low‐risk WT since the International Society of Paediatric Oncology (SIOP) 93‐01 study, and patients have been treated with reduced postoperative therapy. The aim of the study was to evaluate whether the omission of adjuvant chemotherapy in patients with localized CN‐WT stage I and radiotherapy in stage III was safe. Patients and methods The retrospective observational study of outcomes of patients diagnosed with localized CN‐WT on central pathology review and treated according to the SIOP 93‐01 and SIOP‐WT‐2001 protocols (1993–2022). Results There were 125 patients with localized CN‐WT: 90 with stage I, 10 with stage II, and 25 with stage III. Sixty‐two of 125 (49.6%) patients had a discrepant diagnosis and/or staging between the institutional pathologist and central pathology review. In the group of 90 patients with stage I, postoperative chemotherapy was not given to 41 (46%) patients, whereas 49 patients received postoperative chemotherapy—in the latter group, two patients relapsed, and one of them died. One stage I and one stage II patient developed chemotherapy‐induced toxicity and died. Nineteen of 25 patients with stage III received no flank radiotherapy. No stage III patient relapsed or died. The overall 5‐year event‐free survival (EFS) estimate for the entire cohort (stages I–III) was 96.8% 95% confidence interval, CI: 93.6%–99.6% and the overall survival (OS) was 97.6% 95% CI: 95.0–100%. The EFS and OS were 97% and 98%, respectively, for stage I, and 100% for stage III. Conclusion Omission of postoperative chemotherapy for patients with CN‐WT stage I, and radiotherapy for stage III is safe. Rapid central pathology review is required to assign appropriate treatment and avoid treatment‐related side effects.