Prior epidemiological studies have consistently shown a strong association between elevated FGF23 and mortality in non–dialysis-dependent patients with CKD,15, 16, 17, 18, 19, 20 incident hemodialysis patients,21,22 kidney transplant recipients,23,24 and individuals with apparently normal kidney function.25, 26, 27, 28, 29, 30, 31, 32 By contrast, limited data exist on the association between FGF23 and mortality in a large cohort of prevalent hemodialysis patients. The gene discussed is FGF23; the disease is chronic kidney disease.