The islands of the Gulf of California are considered protected natural areas by the Mexican government. However, mammals in these islands face major threats and possible extinction because of the introduction of exotic species. Dipodomys insularis is endemic to San José Island, and has been declared a critically endangered species by the World Conservation Union. Surveys undertaken since 1989 had been unsuccessful in documenting the presence of this species, leading to the conclusion that extinction may have occurred because of the presence of feral cats on the island. After 15 years of unsuccessful surveys, we rediscovered D. insularis in 2005. Kangaroo rats were captured at 5 locations on the island within a total area of less than 30 km². Fecal analyses showed that D. insularis is not a usual prey item of feral cats. A discriminant function analysis allocated 99.29% of the heteromyid upper incisors recovered from scats to Chaetodipus spinatus (P > 0.97), whereas only 2 incisors (0.71%) were allocated to D. insularis. The actual extent of damage to the native biota caused by the introduction of cats remains unknown.