Introduction: Idiopathic hypercalciuria (IH) has been recognized as a common disorder in childhood and is an important and common factor in formation of renal stones. Recurrent urinary tract infection is a clinical presentation of hypercalciuria. Regarding that Hydrochlorothiazide is effective in hypercalciuria treatment; therefore in this study we assessed the efficacy of Hydrochlorothiazide in preventing recurrent UTI in hypercalciuric girl patients.Materials & Methods: This research was a single blind randomized clinical trial.100, 1 to 12 years old girls, who were followed by pediatric nephrology outpatient clinic in Vali- Asr and Arnir Kabir hospitals, with the diagnosis of idiopathic hypercalciuria and at least two urinary tract infections in year, were included in study.Patients were randomly divided in to two equal groups. First group received a general preventive treatment consisted of a liberal fluid, urination every 2 hours, reducing dietary salt intake, washing genitalia from front to back, wearing cotton loose underwear and complete urination. In second group, in addition to the general treatment, Hydrochlorothiazide was used with initial dose of 1mg/kg/day in a morning dosage. Then, urinary tract infection recurrence in two groups was assessed by student T test.Results: All patients who received Hydrochlorothiazide were normocalciuric. In each group, incidence of UTI non recurrence was 34% (17cases), that was not significantly different.Conclusion: This study rejected the presence of hypercalciuria treatment effect in preventing recurrent urinary infection. There fore, the association between UTI and IH needs to be close lystudied with the attention to eliminate confounding factors.