This investigation of XLH and TIO in adults complements a recent retrospective comparison of the presentations of XLH and tumor‐induced osteomalacia/rickets in a cohort of children in China.(10) In agreement with our results, this study also identified serum phosphorus, serum ALP, FGF23, and lumbar spine BMD as important differentiators of the two diseases in pediatric patients. The gene discussed is FGF23; the disease is osteomalacia.