The distribution of Allen’s Swamp Monkey, is centred on the lowland forests of the central Congolian basin - Democratic Republic of the Congo (both sides of the Congo River), Cameroon and Congo (Kingdon 2001; Maisels et al. 2006). Allen’s Swamp Monkeys are recorded on two islands in the Sangha River near the village of Bomassa (Maisels et al. 2006). The known limits of its east-west distribution are from about 16°E to about 26º–27°E, and its north-south distribution from about 3°N to 6°30′ S (Kingdon 2001). It may be present in north-eastern Angola, although this requires confirmation.