Autosomal dominant hypophosphatemic rickets (ADHR) is remarkable among the hypophosphatemic rickets syndromes for its variable age of presentation and periods of quiescence during which serum phosphate and fibroblast growth factor 23 (FGF 23) levels are normal without therapy. In contrast, hypophosphatemia in X-linked hypophosphatemic rickets (XLH) manifests soon after birth and requires lifelong therapy. This suggests that there are environmental factors which can alter FGF 23 activity in ADHR but not in XLH. We present an adult with ADHR in whom resolution of hypophosphatemia was achieved by correcting iron deficiency without the need for phosphate supplementation. Serial iron and FGF 23 levels revealed an inverse relationship (r = −0.79, p < 0.04). All patients with ADHR who present with hypophosphatemia and worsening symptoms should be screened for iron deficiency. If iron deficiency is detected, therapy with a combination of calcitriol and iron supplementation should be considered without phosphate supplementation.