Objective: To find out if cardiovascular alterations are present in pediatric patients with X-linked hypophosphatemia (XLH). Study design: Multicentre prospective clinical study on pediatric patients included in the RenalTube database (www.renaltube.com) with genetically confirmed diagnosis of XLH by mutations in the PHEX gene. The study’s protocol consisted of biochemical work-up, 24-h ambulatory blood pressure monitoring (ABPM), carotid ultrasonography, and echocardiogram. All patients were on chronic treatment with phosphate supplements and 1-hydroxy vitamin D metabolites. Results: Twenty-four patients (17 females, from 1 to 17 years of age) were studied. Serum concentrations (X ± SD) of phosphate and intact parathyroid hormone were 2.66 ± 0.60 mg/dl and 58.3 ± 26.8 pg/ml, respectively. Serum fibroblast growth factor 23 (FGF23) concentration was 278.18 ± 294.45 pg/ml (normal < 60 pg/ml). Abnormally high carotid intima media thickness was found in one patient, who was obese and hypertensive as revealed by ABPM, which disclosed arterial hypertension in two other patients. Z scores for echocardiographic interventricular septum end diastole and left ventricular posterior wall end diastole were + 0.77 ± 0.77 and + 0.94 ± 0.86, respectively. Left ventricular mass index (LVMI) was 44.93 ± 19.18 g/m 2.7 , and four patients, in addition to the obese one, had values greater than 51 g/m 2.7 , indicative of left ventricular hypertrophy. There was no correlation between these echocardiographic parameters and serum FGF23 concentrations. Conclusions: XLH pediatric patients receiving conventional treatment have echocardiographic measurements of ventricular mass within normal reference values, but above the mean, and 18% have LVMI suggestive of left ventricular hypertrophy without correlation with serum FGF23 concentrations. This might indicate an increased risk of cardiovascular involvement in XLH.