Deranged calcium-phosphate metabolism contributes to the burden of morbidity and 
mortality in dialysis patients. This study aimed to assess the association of 
the phosphaturic hormone fibroblast growth factor 23 (FGF23) and soluble Klotho 
with all-cause mortality. We measured soluble Klotho and FGF23 levels at 
enrolment and two weeks later in 239 prevalent hemodialysis patients. The 
primary hypothesis was that low Klotho and high FGF23 are associated with 
increased mortality. The association between Klotho and atrial fibrillation (AF) 
at baseline was explored as secondary outcome. AF was defined as presence of 
paroxysmal, persistent or permanent AF. During a median follow-up of 924 days, 
59 (25%) patients died from any cause. Lower Klotho levels were not associated 
with mortality in a multivariable adjusted analysis when examined either on a 
continuous scale (HR 1.25 per SD increase, 95% CI 0.84-1.86) or in tertiles, 
with tertile 1 as the reference category (HR for tertile two 0.65, 95% CI 
0.26-1.64; HR for tertile three 2.18, 95% CI 0.91-2.23). Higher Klotho levels 
were associated with the absence of AF in a muItivariable logistic regression 
analysis (OR 0.66 per SD increase, 95% CI 0.41-1.00). Higher FGF23 levels were 
associated with mortality risk in a multivariable adjusted analysis when 
examined either on a continuous scale (HR 1.45 per SD increase, 95% CI 
1.05-1.99) or in tertiles, with the tertile 1 as the reference category (HR for 
tertile two 1.63, 95% CI 0.64-4.14; HR for tertile three 3.91, 95% CI 
1.28-12.20). FGF23 but not Klotho levels are associated with mortality in 
hemodialysis patients. Klotho may be protective against AF.