Abstract Background and Aims X-linked hypophosphatemic rickets (XLH) is a genetic disorder secondary to the mutation of the PHEX gene that results in increased circulating levels of FGF23. Increased FGF23 causes hypophosphatemia secondary to renal phosphate loss. Clinically, the disease is characterized by reduced growth, bone alterations, weakness, chronic pain and reduced mobility. From a biochemical point of view, patients have hypophosphatemia, increased values of alkaline phosphatase, increased fraction excretion of phosphate (FEP). Recently, therapy with Burosumab, a monoclonal antibody against FGF23, has been introduced. Burosumab by reducing the receptor availability of circulating FGF23 reduces its activity. This leads to a normalization of serum phosphate and in paediatric patients an improvement of the clinical phenotype. In adult patients, the effectiveness of therapy in improving the clinical outcome and quality of life is being investigated. The purpose of the study was to evaluate the efficacy in improving the biochemical, bone and clinical picture of adult patients with XLH in therapy with Burosumab for one year. Method We enrolled patients with XLH naive for Burosumab therapy. In all we evaluated the biochemical aspects (phospahatemia, alkaline phosphatase, FEP), bone Radiographic Global Impression of Change score and clinical improvements (six-minute walk test, UP and go timed test, WOMAC Index) pre therapy and after a year of therapy. Burosumab was administered monthly at a dose of 1 mg/Kg. Results We enrolled 5 patients (45 ± 10 year old, weight 60 ± 10 Kg, Burosumab dose 60 ±10 mg) with genetic diagnosis of XLH. The comparison between pre therapy and post-one-year therapy showed in all patients: increase in average phosphatemia (pre 1.9± 0.5 mg/dl vs post 3.4 ±0.6 mg/dl p = 0.003), reduction in FEP (pre 50 ±15% vs 20 ±10% p = 0.004), reduction of UP and go timed test (pre 20± 5 sec vs post 11 ±5 sec p = 0.005) increase of the distance in the six minutes’ walk test (pre 150 ± 30 meters vs post 250 ± 50 meters p = 0.01), improvement of the WOMAC test (pre 15± 3 vs post 5± 2; p = 0.008) and reduction of the Radiographic Global Impression of Change score (pre -2 ±0.5 and post 2± 0.4; p = 0.001). The serum value of alkaline phosphate was high and it did not change with the Burosumab therapy (pre 200±50 UI/L vs post 220±60 UI/L; p: n.s. n.v. 33–98 UI/L). No patients had significant complications during the first year of treatment. Conclusion The therapy with Burosumab was well tolerated by patients. It resulted in a marked improvement in the biochemical picture associated with a better quality of life identified by increased strength (improved walk test and UP and go timed test) reduction of pain (best WOMAC test) and bone damage score. In conclusion, Burosumab may be a good and safe therapy option for adults’ patients with XLH.