An updated list of the mammals of Chihuahua state, Mexico was assembled from the literature and from museum specimens. We documented 133 species (15 endemic to Mexico and 11 new for Chihuahua), representing 25 families, 75 genera, and 27.4% of the Mexican terrestrial mammalian fauna. Four species are probably extirpated from the state. Four major ecoregions have been defined for Chihuahua: Arid, Valleys, Sierra, and Quebradas. Species richness was the highest in Valleys, and consisted mostly of species with Nearctic affinities. In contrast, Quebradas were the least species-rich, but included mostly Neotropical species that occur only in this ecoregion of Chihuahua. Despite the fact that Chihuahua harbors considerable biodiversity and unique Mexican biomes, conservation efforts are insufficient. The current rate of anthropogenic modification in the state requires a comprehensive strategy if Chihuahua’s biodiversity is to be preserved.