A nationwide epidemiologic survey of fibroblast growth factor 23 (FGF23)-related hypophosphatemic diseases was conducted in 2010 to clarify the prevalence and the clinical presentations of the disorders. A questionnaire inquiring the experience of patients with these diseases was sent to randomly selected hospitals throughout Japan. The estimated annual incidence of the diseases was 117 cases (95% CI 75 - 160), 55 males (95% CI 30 - 81) and 62 females (95% CI 40 - 84). Tumor-induced osteomalacia (TIO) and X-linked hypophosphatemic rickets (XLH) were the most prevalent causes of acquired and genetic FGF23-related hypophosphatemic diseases, respectively. The estimated incidence of XLH was about 1 in 20,000. We have also collected clinical data of the patients by a secondary survey. These patients showed FGF23 levels of above 30 pg/mL by intact assay in the presence of hypophosphatemia. While complete resection of responsible tumors improved biochemical abnormalities in patients with TIO, treatment with phosphate and/or active vitamin D3 did not normalize serum phosphate and tubular maximum transport of phosphate in patients with XLH. Our results suggest that there is no racial difference in the incidence of XLH. While FGF23 measurement is useful for the diagnosis of FGF23-related hypophosphatemic diseases, the better management is necessary especially for patients with genetic hypophosphatemic rickets caused by excessive actions of FGF23.