Nephrogenic Diabetes Insipidus (NDI) is a type of Diabetes Insipidus (DI) where distal nephrons are unresponsive to antidiuretic hormone resulting in polyuria and polydipsia. NDI can be congenital or acquired. There are very few cases of congenital NDI, more in sibs. Here we report two sibs affected with congenital NDI. Both of them presented with polyuria, polydipsia and failure to thrive since early infancy.