Autosomal dominant familial neurohypophyseal diabetes insipidus (adFNDI) is a rare form of central diabetes insipidus (DI), and this malady is clinically characterized by polydipsia and polyuria, and it is caused by mutation in the vasopressin-neurophysin II. We identified a Korean family that suffered with adFNDI and we found a novel mutation in the NP II molecule. The index subject’s DI symptoms dated to childhood, and his familial history was consistent with autosomal transmission. The diagnosis of central DI was done by performing a water deprivation test and a vasopressin challenge test. For molecular analysis, the genomic DNA was ext racted and the AVP-NP II gene was amplified by polymerase chain reaction from four clinically-affected members and seven clinically-nonaffected members. Genetic analysis of AVP-NP II revealed new a heterozygous missense mutation in exon 2 of the AVP-NP II gene (+1692C > A) and this amino acid substitution (Cys105Stop) was predicted to have occurred in four clinically-affected subjects. In summary, in the present study we have described a novel mutation of the AVP-NPII gene in a Korean family suffering with adFNDI. (J Kor Endocrine Soc 22:118~124, 2007)