Abstract Our study aimed to assess the role of fibroblast growth factor 23 (FGF-23) as a prognostic marker after an acute coronary syndrome (ACS). It was a prospective and multicentric study, performed at five tertiary hospitals in our city, which included 1,190 patients with ACS. FGF-23 plasma levels and other components of mineral metabolism (calcidiol, parathormone [PTH], klotho, and phosphate), lipids, troponin, high-sensitivity C-reactive protein, and N-terminal-pro-brain natriuretic peptide were measured at discharge. The primary outcome was a combination of acute ischemic events, heart failure (HF) and death. Secondary outcomes were the separate components of the primary outcome. Median follow-up was 5.44 (3.03-7.46) years. 294 patients developed the primary outcome. Patients with FGF-23 less than median (which was settled in 110 RU/mL) were less frequently females, and were younger and had a lower load of cardiovascular risk factors. Besides, calcidiol and PTH levels were lower in patients with FGF-23 below the median. Multivariable analysis showed that FGF-23 (HR 1.18 [1.08-1.29], p<0.001), calcidiol (HR 0.86 [0.74-1.00], p=0.046), previous CAD or cerebrovascular accident, and hypertension were independent predictors of the primary outcome. The predictive power of FGF-23 was homogeneous across different subgroups of population. FGF-23 resulted an independent predictor of HF (HR 1.38 [1.22-1.57], p<0.001), and death (HR 1.21 [1.07-1.37], p=0.002), but not of acute ischemic events. According to renal function, FGF-23 was an independent predictor for the primary outcome in patients with estimated glomerular filtration rate (eGFR) above 60 ml/min/1.73m2,, showing that the potential prognostic role of FGF-23 was not exclusively related to chronic kidney disease patients. Moreover, regarding the secondary outcomes, FGF-23 resulted an independent predictor of HF and death. To sum up, FGF-23 seems to be a strong, independent, predictor of HF and death among patients with ACS. This effect is homogeneous across different subgroups of population and not limited to patients with CKD.