A screen of recessive mutations generated by the chemical mutagen n-ethyl-n-nitrosourea (ENU) mapped a new mutant locus (5772SB) termed sudden juvenile death syndrome (sjds) to chromosome 7 in mice. These mutant mice, which exhibit severe proximal tubule injury and formation of giant vacuoles in the renal cortex, die from renal failure, a phenotype that resembles aquaporin 11 (Aqp11) knockout mice. In this report, the ENU-induced single-nucleotide variant (sjds mutation) is identified. To determine whether this variant, which causes an amino acid substitution (Cys227Ser) in the predicted E-loop region of aquaporin 11, is responsible for the sjds lethal renal phenotype, Aqp11−/sjds compound heterozygous mice were generated from Aqp11+/sjds and Aqp11+/− intercrosses. The compound heterozygous Aqp11−/sjds offspring exhibited a lethal renal phenotype (renal failure by 2 wk), similar to the Aqp11sjds/sjds and Aqp11−/− phenotypes. These results demonstrate that the identified mutation causes renal failure in Aqp11sjds/sjds mutant mice, providing a model for better understanding of the structure and function of aquaporin 11 in renal physiology.