Necromys is a genus of sigmodontine rodent widely distributed throughout South America, from central Argentina to Trinidad and Tobago, and includes eight living species. In Brazil, two species are currently known: Necromys lasiurus, widely distributed, and Necromys lenguarum, known only from a sole locality in Mato Grosso state, core area of Cerrado domain, based on its putative junior synonymy, Zygodontomys tapirapoanus. The latter species have been previously recorded in Bolivia, Paraguay, Argentina, and Peru, but many authors did not acknowledge the presence of the species in Brazil. Based on molecular data (mitochondrial gene Cytochrome b), we present five new localities of the here recognized N. lenguarum, along with new samples of N. lasiurus from sympatric and parapatric localities. Voucher specimens of N. lasiurus and N. lenguarum had their identification confirmed by molecular data, followed by morphological comparison with representatives of other Necromys species, including type specimens. These results prompted new insights into morphology and geographic distribution of N. lenguarum, and revealed that the characters currently proposed as diagnostic for N. lenguarum failed to distinguish it from the N. lasiurus (Lund, 1840). Since that we found syntopy of the two species and the type locality of N. lenguarum fall within the distribution range of N. lasiurus sequenced specimens, in absence of DNA sequence of the N. lenguarum holotype, the taxonomic identity of populations until now referred to N. lenguarum still require further analyses including DNA sequence from its holotype. Furthermore, both species are involved in distinctive zoonotic cycles and were found in syntopy in a new locality, highlighting the importance of better delimitate cryptic species.2022-01-01