The aims of this study were to determine longitudinal changes in C-FGF23 concentration and cross-sectional predictors of I-FGF23 and C-FGF23 concentrations in Gambian children with and without a history of rickets and to determine whether circulating FGF23 concentration and dietary Ca intake are determinants of the half-life of 25-hydroxyvitamin D (25OHD-t1/2). The gene discussed is FGF23; the disease is rickets.