AbstractMarmosa subgenus Micoureus contains six currently recognized species, distributed from southern Belize to northern Argentina. Although recent studies have demonstrated the monophyly of the subgenus, the species have not been recently revised. Except for M. phaea, we evaluated the species diversity in this subgenus of mouse opossums using integrated morphological, morphometric and molecular data, with emphasis on M. constantiae. We used a total of 700 specimens for morphological and morphometric analyses. For phylogenetic, species delimitation, molecular variance and population structuring analyses (the latter two only for M. constantiae), we used the mitochondrial cytochrome b gene. Morphometric variation patterns were evaluated through Principal Component Analysis and Discriminant Function Analysis. Our results indicate that there are seven species in our samples. Among the species analysed morphologically, some can be discriminated by craniodental measurements and all can be discriminated through morphology. Marmosa constantiae is polyphyletic, composed of two lineages, one of which is correctly named M. budini. Marmosa constantiae (s.s.) has a well-known genetic structure, with no clear geographic structure and no consistent morphological patterns. Several records of M. demerarae in the literature correspond to M. constantiae. Marmosa demerarae may thus represent a complex formed of at least two species.