AbstractPURPOSE:To compare the characteristics and outcome of adults and children diagnosed with Wilms' tumor.METHODS:The Surveillance, Epidemiology and End Results (SEER) database was analyzed for patients diagnosed with Wilms' tumor between 1973 and 2007. Patients were stratified into pediatric (<16 years) or adult (≥16 years) groups. Overall survival was the primary endpoint.RESULTS:A total of 2342 patients (2190 pediatric and 152 adult) with Wilms' tumor were identified. Adult patients were statistically more likely to be staged as localized than pediatric patients (62.5% vs 44.7%), to not receive any lymph node sampling (57.9% vs 16.2%), and to not receive any radiation treatment (74.3% vs 53.9%). Adults had a statistically worse overall survival (OS) than pediatric patients (5‐year OS, 69% vs 88%, P<.001) despite the earlier tumor stage. When stratified by treatment era, the OS of all patients treated after 1981 was statistically higher than those treated before (5‐year OS, 75% vs 89%, P<.001). Significant predictors of OS on univariate analysis for adults included treatment era, SEER stage, surgery, and radiation treatment. Significant predictors of OS on multivariate analysis of all patients included adult status (hazard ratio, 4.14; P<.001), treatment era, SEER stage, and surgery.CONCLUSION:Adults in the SEER database had statistically worse OS than pediatric patients despite previous studies showing comparable outcome when treated on protocol. The worse outcome of SEER adults likely stems from incorrect diagnosis, inadequate staging and undertreatment. We recommend lymph node samplings for all adult Wilms' tumor patients and collaboration with pediatric oncologists. Cancer 2012. © 2011 American Cancer Society.