X-linked nephrogenic diabetes insipidus (NDI) is a rare disease caused by mutations in the vasopressin V2 receptor (AVPR2) gene. We analyzed the AVPR2 gene in 6 unrelated Korean families with X-linked NDI, and found 6 novel mutations. Two of them were missense point mutations, 2 were short deletions causing frameshifts, 1 was a duplication of 9 bases, and 1 was a compound gene rearrangement. Four mutations cosegregated with the clinical phenotype in corresponding family members, and one was a de novo mutation. In 1 family, prenatal diagnosis was made by amniocentesis. In conclusion, we found 6 novel mutations in the AVPR2 gene causing X-linked NDI in 6 families, and direct mutational analysis is now applicable for carrier detection and early (prenatal) diagnosis.