Objective: Hypophosphatemic rickets (HR) is a rare renal phosphate-wasting disorder, which is usually X-linked and is commonly causedby PHEX mutations. The treatment and follow-up of HR is challenging due to imperfect treatment options.Methods: Here we present nationwide initial and follow-up data on HR.Results: From 24 centers, 166 patients were included in the study. Genetic analysis (n=75) showed PHEX mutation in 80% of patients.The mean follow-up period was 6.7±2.4 years. During the first 3-years of treatment (n=91), mild increase in phosphate, decrease inalkaline phosphatase and elevation in parathyroid hormone (PTH) levels were detected. The height standard deviation scores were -2.38,-2.77, -2.72, -2.47 at initial, 1st, 2nd and 3rd year of treatment, respectively (p>0.05). On follow-up 36% of the patients showed completeor significant improvement in leg deformities and these patients had similar phosphate levels at presentation with better levels in 1stand 2nd years of treatment; even the treatment doses of phosphate were similar. Furthermore, 27 patients developed nephrocalcinosis(NC), the patients showed no difference in biochemical differences at presentation and follow-up, but 3rd year PTH was higher. However,higher treatment doses of phosphate and calcitriol were found in the NC group.Conclusion: HR treatment and follow-up is challenging and our results showed higher treatment doses were associated with NC withoutany change in serum phosphate levels, suggesting that giving higher doses led to increased phosphaturia, probably through stimulationof fibroblast growth factor 23. However, higher calcitriol doses could improve bone deformities. Safer and more efficacious therapiesare needed.