A new species of shrew tenrec (Microgale) is described from the central western and southwestern portion of Madagascar. Based on pelage, morphology, and DNA sequence data, this new species can be readily distinguished from its sister taxon, M. brevicaudata. Mitochondrial DNA (mtDNA) divergences between the 2 species are on par with those observed in other closely related shrew tenrecs, and both taxa are recovered as reciprocally monophyletic haplotype clades. Furthermore, mtDNA sequence obtained from the holotype of Paramicrogale occidentalis confirms that the name occidentalis cannot be assigned to the new taxon and is a junior synonym of M. brevicaudata. Microgale new species and M. brevicaudata have latitudinally overlapping distributions, and although they are not known to occur in direct sympatry, specimens of both species have recently been collected at sites within 50 km of each other on opposite sides of the Soahany River in central western Madagascar. However, the respective distributions of these 2 species, among the most diminutive of Madagascar's endemic terrestrial mammal fauna, suggest that rivers do not serve as significant barriers to dispersal. Historical demographic analysis under a coalescence framework suggests that the northerly distributed M. brevicaudata has experienced a recent population expansion, whereas the new species described herein has undergone a population decline. Little is known about the ecology of Microgale new species, but it lives in dry forest formations. This species is known from sites within several protected areas (Bemaraha and Namoroka), as well as forest parcels currently proposed as new conservation zones. However, toward the southern limit of its known distribution, at the north bank of the Onilahy River, there is continued extensive anthropogenic habitat loss that may warrant future monitoring.