The Angel de la Guarda deer mouse Peromyscus guardia on Estanque Island, in the Angel de la Guarda archipelago of the Gulf of California, was probably driven to extinction by a single introduced domestic cat. P. guardia was trapped on the island in October 1995, at which time the species was still relatively abundant. In 1998 a domestic cat was spotted on the island; no deer mice were found at that time nor during subsequent field work in 1999 and 2001. In 1998, c. 100 cat scats were collected, 2% of which contained P. guardia bone remains and 90% P. guardia hair. The cat, which was eradicated in 1999, was the only introduced predator on the island. Our results confirm the extreme vulnerability of island rodent populations to the introduction of alien mammalian predators. To our knowledge, apart from the extermination of Stephens Island wren Xenicus lyalli in New Zealand in 1894 by the lighthouse keeper's cat, this is the first report of the destruction of the total population of an insular species by a single cat. With two of the three subspecies of P. guardia now extinct the only potentially extant population is on the larger Angel de la Guarda Island, where the species was last seen in 1991. A comprehensive survey of the island is required, with subsequent action for the species recovery and conservation if it is found to be extant.