Cases of supernumerary teeth and odontogenic masses in Rodentia are well documented in the literature, but statistically are still relatively uncommon findings. Odontogenic lesions present rarely in rodent families Cricetidae and Muridae, though extra teeth have been documented in Saccostomus, Mesembriomys, Zapus, Baiomys, Peromyscus, Mus, Orzomys, Microtus, and Necromys. The authors here report a possible example of atavistic diastemal teeth in a specimen of Peromyscus (Rodentia: Cricetidae) preserved in the teaching museum collections of Northern Illinois University NIU. To explore frequency of dental anomalies in Peromyscus, we examined a large population of 396 P. leucopus and 51 P. maniculatus housed in the collections of the Chicago Field Museum of Natural History and University of Alberta Museum of Zoology. Only one additional case was found, highlighting the probable rarity of such pathologies in this genus.