X-linked hypophosphatemic rickets (XLH), autosomal dominant hypophosphatemic rickets, hereditary hypophosphatemic rickets with hypercalciuria, and tumor-ind uced osteomalacia share clinical and biochemical features, and are collectively referred to as hypophosphatemic rickets (HR). Recently, the molecular bases of H R were elucidated. A review of medical records and mutational analyses of the PH EX and FGF23 genes were performed on 17 unrelated Korean children with HR. The m ale-to-female ratio was 3:14, and 5 patients were familial. Initial laboratory tests revealed typical features of HR. Seven different PHEX mutations were dete cted in 8 patients: 2 missense mutations, 2 nonsense mutations, and 3 short dele tions. No functional FGF23 mutation was detected in any patient. Patients with t he PHEX mutation tended to have more severe skeletal disease than those without. Of the patients with this mutation, no genotype-phenotype correlation and no g ene dosage effect were noted. Treatment with vitamin D and phosphate resulted in only a partial growth improvement in most cases, and was frequently complicated by hypercalciuria, hypercalcemia, nephrocalcinosis, or hyperparathyroidism. Ren al glycosuria was detected in six cases and was associated with more severe skel etal disease. We conclude that current HR treatment is not fully safe or effecti ve, and that close monitoring of treatment effectiveness and for complications s hould be performed during long-term treatment. No genotype-phenotype correlati on in XLH was detected in this study, but a large-scaled study on this topic is warranted. The large proportion of patients with a normal genetic study suggest s the possibility of other causative gene(s). X-linked hypophosphatemic rickets (XLH), autosomal dominant hypophosphatemic rickets, hereditary hypophosphatemic rickets with hypercalciuria, and tumor-indcedcedomasscia share clinical and biochemical features, and are collectively referred to as hypophosphatemic rickets (HR). Recently, the molecular bases of HR was elucidated. A review of medical records and mutational analyzes of the PH EX and FGF23 genes were performed on 17 unrelated Korean children with HR. The m ale-to-female ratio was 3:14, and 5 patients were familial. Initial laboratory tests revealed typical features of HR. Seven different PHEX mutations were dete cted in 8 patients: 2 missense mutations, 2 nonsense mutations, and 3 short deletions. No functional FGF23 mutation was detected in any patient. Patients with he PHEX mutation tended to Of the patients with this mutation, no genotype-phenotype correlation and no g ene dosage effect were noted. Treatment with vitamin D and phosphate resulted in only partial growth improvement in most cases, and was frequently complicated by hypercalciuria, hypercalcemia, nephrocalcinosis, or hyperparathyroidism. Ren al glycosuria was detected in six cases and was associated with more severe skel etal disease. We conclude that current HR treatment is not fully safe or effecti ve, and that close monitoring of treatment effectiveness and for complications s hould be performed during long-term treatment. No genotype-phenotype correlati on in XLH was detected in this study, but a large- scaled study on this topic is warranted. The large proportion of patients with a normal genetic study suggest s the possibility of other causative gene (s).