Transgenic mouse models of defective urinary concentrating ability produced by deletion of various membrane transport or receptor proteins, including aquaporin-2 (AQP2), are associated with neonatal mortality from polyuria. Here, we report an inducible mouse model of AQP2 gene deletion with severe polyuria in adult mice. LoxP sequences were inserted into introns 1 and 2 in the mouse AQP2 gene by homologous recombination in embryonic stem cells. Mating of germ-line AQP2-loxP mice with tamoxifen-inducible Cre-expressing mice produced offspring with inducible homozygous Cre-AQP2-loxP, which had normal phenotype. Tamoxifen injections over 10 days resulted in AQP2 gene excision, with undetectable full-length AQP2 transcript in kidney and >95 % reduction in immunoreactive AQP2 protein. Urine osmolality decreased from ~ 2000 to < 500 mOsm after 4-5 days, with urine output increasing from 2 to 25 ml/day. Urine osmolality did not increase after water deprivation. Interestingly, AQP3 protein expression in collecting duct was increased by >5-fold after AQP2 gene excision. Mild renal damage was seen after 6 weeks of polyuria, with collecting duct dilatation, yet normal creatinine clearance and serum chemistries. These results establish the first adult model of NDI caused by AQP2 deficiency, with daily urine output comparable to body weight, though remarkable preservation of renal function compared to non-inducible NDI models.