Dent's disease is a hereditary renal tubular disorder caused by mutations of the CLCN5 gene and is clinically characterized by low molecular weight proteinuria, hypercalciuria and nephrocalcinosis. This disease has been reported in several countries. However, there are some phenotypic differences between countries, such as hypophosphatemic rickets, progressive renal failure and hematuria. In this study, phenotypes were analyzed in three Korean boys with Dent's disease, and genetic diagnoses were performed using a new convenient method using peripheral blood RNA. Gene studies revealed two nonsense mutations, R637X in two patients and E609X in one patient. The phenotypes of the two patients with R637X were very similar to those of Japanese patients, i.e., they presented with asymptomatic proteinuria without rickets, renal failure or hematuria. The E609X patient was diagnosed genetically at 3 months of age before the onset of clinical symptoms because of superimposed furosemide-induced nephrolithiasis. This is the first report to characterize mutations in the CLCN5 gene in Korean patients with Dent's disease, and expands the spectrum of CLCN5 mutations by reporting a novel mutation, E609X. In addition, the mutational analysis using peripheral blood RNA can be easily applied in the clinical diagnosis.