ABSTRACTBackgroundThe relationships among treatment exposures, body composition, and estimated glomerular filtration rate (eGFR) in adult survivors of Wilms tumor have not been well studied.MethodsWe evaluated body composition with dual‐energy x‐ray absorptiometry (DXA) and eGFR with the updated Chronic Kidney Disease Epidemiology Collaboration equations (creatinine only—eGFRCr, cystatin C only—eGFRCysC, creatinine and cystatin C—eGFRCr+CysC) without race in 134 adults previously treated for unilateral, non‐syndromic Wilms tumor at St. Jude Children's Research Hospital between 1964 and 2004 with chemotherapy and with (hemiabdomen [HA] or whole abdomen [WA]) or without radiation therapy (RT). Z‐scores for DXA variables were calculated using data from the National Health and Nutrition Examination Survey.ResultsWART was associated with a lower relative total (p = 0.004) and trunk (p < 0.001) lean mass, eGFRCr (p = 0.008), eGFRCysC, (p < 0.001), and eGFRCr+CysC (p < 0.001), and higher values of cystatin C (p < 0.001). Linear regression demonstrated that relative total lean mass (p = 0.009) and relative trunk lean mass (p < 0.001) Z‐scores, and eGFRCr (p = 0.013) were lower among those who received WART compared to No RT patients.ConclusionsWART is associated with lower relative total and trunk lean mass Z‐scores and eGFR, regardless of the equation used, and is lower in survivors treated with WART compared to unirradiated survivors of unilateral, non‐syndromic WT. Assessments using other GFR measures may provide greater insight into the mechanism and magnitude of kidney function loss among WART‐treated WT survivors.