AVPR2 and Polydipsia: Mutations in AVPR2 cause 90% of congenital NDI cases and occur at a frequency of 4 to 8 per 1 million live male births.[1] NDI is commonly diagnosed based on characteristic findings such as polyuria, polydipsia, fever of unknown etiology, convulsions, vomiting, and constipation in early infancy.[3] The diagnosis of NDI is often delayed and intellectual disability may occur as a consequence of delayed treatment.[1] In our case, the diagnosis of NDI was delayed because of a lack of other signs, such as vomiting and fever, although poor body weight gain was recognized after birth.