PURPOSE: Wilms' tumor is the most common malignant tumor of the kidney during the childhood period. This is a potentially curable disease with an excellent prognosis due to the development of the multimodal treatments, including chemotherapy, radiotherapy and nephrectomy. The aim of this study was 1) to analyze our clinical experiences with of Wilms' tumor at a single tertiary medical center, including the survival rate and recurrence of disease after treatment and 2) to investigate the prognostic factors affecting the survival of patients. METHODS: We performed retrospective analysis of the clinicopathologic data of 68 patients who underwent operation for Wilms' tumor during 20 years from March 1986 to March 2005 at Yonsei Medical Center. RESULTS: 40 (58.8%) patients were male and 28 patients (41.2%) were female. The median age at diagnosis was 25 month (range: 2 month to~10 year 10 month). Preoperative neoadjuvant chemotherapy was given in 27 patients (39.7%), and initial nephrectomy followed by chemotherapy was performed in 41 patients (60.3%). Postoperative adjuvant radiotherapy was performed in 27 patients (39.7%). The median duration of follow-up period was 8 year 2 month (range: 24 day to~18 year 6 month). The overall 5-year survival rate and 5-year disease free survival rate were 87.0% and 76.9%, respectively. Univariate analysis showed that the significant prognostic factors affecting survival were age at diagnosis (P=0.016), pathologic stage (P=0.032) and, Tumor spillage or rupture during operation (P=0.005) and tumor cell anaplasia (P=0.031). Multivariate analysis showed that tumor spillage or rupture during operation was the most significant prognostic factor (Relative Risk=4.5). CONCLUSION: Early diagnosis, meticulous surgical technique and proper pre-or postoperative adjuvant chemotherapy and radiotherapy according to the tumor histology significantly increase the patient's survival rates.