Given the uneven and biased nature of present understanding of geographic distributions of mammal species, tools for extrapolating from what is known to a more general prediction would be most useful. We used the genetic algorithm for rule-set prediction (GARP) to generate ecological niche models that were then projected onto geography to predict potential geographic distributions for 17 mammal species of Insectivora, Chiroptera, Rodentia, and Artiodactyla in Oaxaca, Mexico. GARP depends on point occurrence localities from museum records of species, along with electronic maps describing features of climate, topography, and vegetation type. Point localities were divided in 2 sets: one of localities from museum records dated before 1960, which was used to generate the predicted distributions, and the other of localities of museum records resulting from recent inventories (post-1960), which was used to test model accuracy. Predicted distributions for 11 of 17 species were statistically significantly more coincident with independent test points than random expectations; tests for the remaining 6 species would have required larger numbers of test localities to establish significance. GARP is a robust tool for modeling species' geographic distributions, with excellent potential for applicability to strategies for conservation of mammals in Oaxaca and elsewhere.