An inhabitant of the savanna woodlands of west and central Africa. In Sierra Leone, it was formerly the commonest duiker species in the northern savanna and in farm bush on its southern edges; the replacement of primary forest with farm bush and other secondary vegetation has enabled this species to expand its range southwards to some extent (East 1999).

This species formerly occurred throughout the band of savanna woodlands and forest-savanna mosaics north of the main tropical forest belt in West and Central Africa from southern Senegal and The Gambia to the Nile Valley in South Sudan and NW Uganda (East 1999, Wilson 2001). A small relict population was discovered in the Bugungu G.R., immediately south of the Murchison Falls N.P. (Allan 1996). The precise boundaries of the range have not been defined (Kingdon and Hoffmann 2013).

About half of the total population of Red-flanked Duiker occurs in and around protected areas, with relatively large numbers in areas such as Niokolo-Koba (Senegal), Comoé, Haut Bandama and Marahoue (Ivory Coast), Mole, Bui and Digya (Ghana), Pendjari and W (Benin), Bouba Ndjida, Benoué and Faro (Cameroon), Manovo-Gounda-St. Floris, and Bamingui-Bangoran (Central African Republic) and Garamba (DR Congo) (East 1999, Kingdon and Hoffmann 2013). However, the effectiveness of protection within these sites varies widely and large declines have been reported from, e.g. Comoé and Haut-Niger NPs (see population section).