Dent disease is X-linked recessive proximal tubulopathy, due to mutations in the CLCN5 gene. It is characterized by low molecular weight proteinuria, hypercalciuria, nephrocalcinosis and progressive renal failure.A seven-year-old boy was referred after endocrinological examination where abdominal ultrasound showed nephrocalcinosis. There were anamnestic data neither of oedema, macrohaematuria, nor polyuria or hypertension. There were also no data of chronic renal failure in the family. We determined: proteinuria (1.8 g/day), elevated urinary excretion of Beta 2 microglobulin, microscopic haematuria, hypercalciuria (8-10 mg/kg/day), nephrocalcinosis, decreased tubular reabsorption phosphate (65%). Values of growth hormone, parathormone on thyroid hormone were normal. Except hypercalciuria, which was registered in the patient's mother, all other analyses performed in family members were between reference values. Diagnosis was finalized by mutation analysis, which showed S244L substitution on CNCL5. Mutation carrier was mother with normal phenotype.Dent disease is rare X-linked nephrocalcinosis. Definitive diagnosis of this proximal tubulopathy which leads to progressive renal damage is not possible without evidence of gene mutation in renal chlorine channel.