Mastiff bats (genus Eumops, family Molossidae) are widely distributed in the neotropics and southern parts of the United States, and form the most taxonomically diverse genus of the family Molossidae with 14 species and six subspecies. The taxonomyof Eumops was treated in two broad studies, and recently, minor taxonomic changes were proposed. Relationships among taxa were historically proposed based on phenetic analyses using biochemical and morphometric data, but a phylogenetic analysis of all species within the genus is lacking. This study proposes a new hypothesis of relationships among most species and subspecies using morphological data and employing cladistic methods. Morphological complexes examined include skull, dentition, tongue, and external morphology; penial data were compiled from literature. The topology of a strict consensus cladogram revealed that one clade is composed of E. perotis E. trumbulli, and is sister to (E. bonariensis E. delticus E. patagonicus E. nanus E. hansae in an unresolved polytomy). A second clade is composed of E. underwoodi E. dabbenei, and a third consists of E. auripendulus and E. maurus, and both are sister to each other. Eumops glaucinus occupies a separate branch in an unresolved polytomy among clades defined above or as sister to E. perotis, E. hansae and E. bonariensis-complex. Results from this study contradict the relationships proposed by previous studies which considered E. auripendulus closer to E. glaucinus, and also disagree with previous outcomes that suggested the non-monophyly of the genus. Results from this study corroborate affinities of E. dabbenei with E. underwoodi, and the uncertain monophyly of E. bonariensis as a polytypic species, supporting the specific status of E. nanus and E. delticus as recently proposed.