FGF23 and osteomalacia: Burosumab is a fully human monoclonal antibody against FGF23 approved for the treatment of XLH (in the US, EU, and Canada, with conditions of approval varying per location).11 In a phase 3 study in adults with XLH, burosumab significantly improved fracture healing, increased serum phosphorus levels and biochemical markers of bone remodeling, and reduced patient‐reported stiffness compared to placebo.12, 13 In the present study, we investigated the effect of treatment with burosumab on histomorphometric indices of osteomalacia in adults with XLH.