A defect in klotho gene expression in the mouse results in a syndrome that resembles human aging, with greatly shortened lifespan, arteriosclerosis, and defective hearing. In an effort to find functional murine variants of klotho, we sequenced the gene and examined renal expression of the secreted and membrane-bound Klotho isoforms from 16 laboratory-derived and 4 wild-derived inbred strains. Among the laboratory-derived strains, no sequence variation was found in any of the exons or intron–exon boundaries. Among the wild-derived strains, we found 45 sequence variants with six resulting in amino acid substitutions. One wild-derived strain, SPRET/Ei, had four amino acid substitutions and higher levels of the membrane form and total klotho mRNA. In addition, the membrane to secreted klotho expression ratio was elevated in three wildderived strains with amino acid substitutions. Interestingly, SPRET/Ei mice have longer lifespans, decreased atherosclerosis risk factors, and better hearing than almost all other mouse strains.