Cynomops (dog-faced bat) generally is regarded as either a monophyletic genus or, in some cases, a subgenus of Molossops. Species limits and phylogenetic relationships within Cynomops, however, remain unresolved due primarily to subtle morphological differences and similarity in size of the small taxa. We used a combination of morphometric analyses for quantifying size variation and molecular data for reconstructing the evolutionary history within Cynomops. Rooting the tree with Eumops hansae produced a clade of Molossops neglectus and M. temminckii that was sister to a monophyletic Cynomops clade. The most parsimonious topology (in parenthetical notation) for Cynomops was (((paranus planirostris) (greenhalli abrasus)) mexicanus). Molecular analysis supports the autapomorphy of white venter as diagnostic for C. planirostris, although there was some overlap in size with the slightly larger, dark-venter C. paranus. Cynomops greenhalli was intermediate in size between C. paranus and C. mexicanus, but molecular analyses placed it as sister to the large-sized C. abrasus. The western Mexico endemic C. mexicanus, traditionally considered a subspecies of C. greenhalli, averaged larger in size than the other small Cynomops taxa and was the most basal lineage, requiring its designation as a distinct species.