To study the possible role of disease in the decline of endangered European mink (Mustela lutreola), we conducted a survey of antibody prevalence and renal carriage of pathogenic leptospira (Leptospira interrogans sensu lato) using serum and kidney samples collected from 1990 to 2007 from several free-ranging small carnivores and farmed American mink (Mustela vison) in southwestern France. An indirect microscopic agglutination test using a panel of 16 serovars belonging to 6 serogroups (Australis, Autumnalis, Icterohæmorrhagiæ, Grippotyphosa, Panama, Sejroe) revealed antibodies in all species, with significant differences in antibody prevalences: 74% in European mink (n=99), 65.4% in European polecats (Mustela putorius, n=133), 86% in American mink (n=74), 89% in stone martens (Martes foina, n=19), 74% in pine martens (Martes martes, n=19), 35% in common genets (Genetta genetta, n=79), and 31% in farmed American mink (n=51). Serogroups Australis and Icterohæmorragiæ were dominant in most free-ranging species; serogroup Grippotyphosa had high prevalences in European mink. Such high antibody prevalences have never been reported. They are probably related to the large number of known reservoirs, rats (Rattus spp.), muskrat (Ondatra zibethicus), and coypu (Myocastor coypu), in the study area. The polymerase chain reaction test specific for pathogenic leptospiral DNA detected renal carriage in 23% of 34 European mink, 22% of 18 polecats, and 15% of 33 free-ranging American mink, with no significant differences. Renal carriage shows that mustelids may shed leptospira for short periods, but their epidemiologic role is probably limited. High antibody prevalences suggest that the disease is unlikely to be highly pathogenic for these species; however, chronic forms of the disease (abortions, renal lesions) could reduce the reproductive success or life span of infected animals. Further studies on the pathogenicity of leptospirosis in these populations are needed to measure its impact on the population dynamics of these rodent predators.