Remaining jaguar Panthera onca populations in the Atlantic Forest are restricted to eight regions, and all populations appear to be declining. We report on the status of one of the last populations in south-eastern Brazil. We monitored this population with camera traps during June 2005–January 2013 in Vale Natural Reserve. We estimated an abundance of 9 ± SE 1.98 jaguars (95% CI 9–17) and a population density of 3.22 ± SE 1.58 individuals per 100 km2 (95% CI 1.29–7.98). Annual survival probability over a 5-year interval was 78% (95% CI 58–98) and the recapture probability was 62% (95% CI 42–79). Although our results are among the highest densities reported for the jaguar in this biome, the future of the population is threatened by genetic deterioration and local threats, including the expansion of an existing highway and depletion of the jaguar's native prey base as a result of poaching, and will depend upon urgent implementation of conservation actions. The necessary actions include establishing gene flow with other compatible populations, increasing surveillance against poaching, continuing population monitoring of jaguars and their main prey species, and implementing mitigation measures in relation to the impacts of the highway on local fauna.