Reintroductions of endangered species are controversial because of high costs and frequent failures. However, the population of black-footed ferrets descended from animals released in Shirley Basin, Wyoming, from 1991 to 1994 has grown rapidly after a decline to a low of five animals in 1997. Beginning around 2000, the population grew rapidly to an estimated 223 (95% confidence interval is 192 to 401) individuals in 2006. Matrix population modeling shows the importance of survival and reproduction during the first year of life, reflecting an uncommon life history for an endangered mammalian carnivore. Recovery of the species may benefit from more opportunistic and widespread releases.