An Ethiopian endemic with 2n = 62, FN = 68 (Corti et al., 1996; Orlov and Bulatova, 1997; Orlov et al., 1992a). Historically the species was perceived to embrace forms occurring from Ethiopia south to Zambia (G. M. Allen, 1939; Dollman, 1911; Ellerman, 1941), but Osgood (1936:252) discussed several of A. abyssinicus's diagnostic features, noting that it "is not unlikely that it is confined to Ethiopia and at least some of the forms of Kenya and Uganda which have been associated with it will need other allocation." This view has been reinforced by analyses of morphometric (Bekele et al., 1993; Corti and Fadda, 1996; Fadda and Corti, 2001; Rousseau, 1983), chromosomal (Baskevich and Lavrenchenko, 2000; Corti et al., 1996b; Orlov et al., 1991a), and mtDNA cytochrome b sequences (Ducroz et al., 1998), as well as our examination of specimens. Yalden and Largen (1992) speculated that A. abyssinicus may also occur in Kenya, Uganda, and elsewhere but no specimens or any other kind of data suggests its distribution extends beyond the Ethiopian Plateau.

Arvicanthis abyssinicus and A. blicki are the only species of Arvicanthis endemic to the Ethiopian Plateau; both are part of middle and high altitude grassland and moorland mammal communities also unique to the plateau (Demeter and Topal, 1982; Rupp, 1980; Yalden, 1988); are more closely related to each other than to any other species of the genus, as judged by morphological, allozymic, and chromosomal traits (Capanna et al., 1996; Capula et al., 1997; Musser and Carleton, 1993); and may have diverged from a common ancestor during the Pleistocene (Capanna et al., 1996b). Both A. abyssinicus and A. blicki are close phylogenetic allies of A. niloticus (which occurs in Ethiopia as well as elsewhere) and the three constitute a monophyletic group (Ducroz et al., 1998; Corti et al., 1996b). Arvicanthis neumanni is another member of the Ethiopian fauna but does not occur on the plateau and also ranges far beyond that country's boundaries.

Rousseau (1983) regarded mearnsi, described as a subspecies of A. abyssinicus by Frick (1914), to be a subspecies of A. abyssinicus, but its qualitative dental and chromatic characteristics fall within the range of variation seen in A. niloticus, as Osgood (1936) and Yalden et al. (1976) noted (discussed by them under either lacernatus or dembeensis).