Objectives: Fibroblast growth factor (FGF)-23 is a key regulator of mineral metabolism and has been linked with left ventricular hypertrophy in animal models. Most existing epidemiologic studies evaluated a C-terminal FGF23 assay which measures both the intact (active) hormone and inactive fragments. The relationship of intact FGF23 with cause-specific mortality is unknown. Design: Prospective analyses of data from Health, Aging, & Body Composition (HABC) study. Setting: Community-living adults aged 70 to 79 years with longitudinal follow up.