Case Study: Dent disease (OMIM #300009) is an X-linked recessive tubulopathy which is characterized by proximal tubule dysfunction including low-molecular-weight proteinuria, hypercalciuria, nephrocalcinosis or nephrolithiasis and rickets. Herein, we report a pediatric case in which the disease was found through asymptomatic proteinuria in school urine screening. A 6-year-old boy was referred to our hospital after three consecutive episodes of proteinuria (once school urine test and twice nearby hospital urine tests). There was no previous past history. In family history, his grandmother experienced urolithiasis several times. After being told that he had proteinuria, the mother took a closer look at her son's urine and saw that the urine had milky cloudy sediment. To rule out orthostatic proteinuria first, proteinuria was compared in the first morning urine and afternoon urine. A similar degree of proteinuria was found in the morning and afternoon urine (In 1st morning urine, urine protein 2+, random protein to creatinine ratio 1.7, in the afternoon urine, urine protein 2+, protein to creatinine ratio 2.0). The serum albumin level was 3.7 g/dL and serum creatinine level was 0.5 mg/dL. He had nephrotic range proteinuria (47 mg/m2/hr) and hypercalciuria (10mg/kg) in 24hr urine test and β-2 microglobulinuria (≥40mg/L) in random urine. There were no abnormal findings on kidney ultrasound. Kidney biopsy was not performed. Instead, Sanger sequencing was directly used for screening for Dent disease. A hemizygotic mutation (c.1564_1566del, p.Val522del) was found in the exon 10 of the CLCN5 gene and the same mutation was detected in his asymptomatic mother. This case highlight the importance of genetic study in the early diagnosis of Dent disease. When patients have proteinuria and/or hypercalciuria, the presence of tubular proteinuria should be checked, and if there is tubular proteinuria, a genetic test should be considered for confirmation prior to kidney biopsy or treatments including steroid.