In the older brother and younger brother, clinical manifestations of diabetes insipidus in the form of severe thirst and polyuria were noted from infancy, after the examination, the diagnosis was made — diabetes insipidus and desmopressin was prescribed.Due to the lack of effect from the use of desmopressin, the analysis of exons and adjacent sections of the introns of the AQP2 and AVPR2 genes was carried out by PCR and subsequent direct sequencing. The gene discussed is AVPR2; the disease is diabetes insipidus.