This species is found from the south and east of the Congo-Oubangui River system in central Africa, through Uganda to the Rift Valley in Kenya and western Tanzania; it ranges as far south as northern Angola to north-western Zambia Gautier-Hion et al. 1999; Butynski 2002). It is known to occur up to 2,000 m.

There are five recognized subspecies:

The subspecies C. a. ascanius is present in Angola and south-western Democratic Republic of the Congo, south of the Congo and Kasai Rivers, generally below 500 m asl. North of this, some animals between the Kasai and Lukenie rivers may be attributable to this form (Sarmiento et al. 2001).

C. a. atrinasus is restricted to the vicinity of the type locality of Zovo, Angola on the Lunda Plateau at about 850 m asl. Although the type locality is near DR Congo, this subspecies has never been recorded from this country (Sarmiento et al. 2001).

The southern subspecies C. a. katangae is present mainly in southern Democratic Republic of the Congo and Angola, between the Kasai and Lualaba Rivers at 500-1,300 m asl (see Sarmiento et al. 2001 for details). It is also reported in north-western Mwinilunga District (Ansell 1978).

C. a. whitesidei is present in the Democratic Republic of Congo where it ranges mostly south and east of the Congo River and west of the Lomami. The Lukenie marks the southern boundary, although monkeys that are similar to this taxon are known from south of the river (Sarmiento et al. 2001).

The eastern subspecies C. a. schmidti has the widest distribution of the five subspecies and occurs from east of the Lualaba River, Democratic Republic of Congo, into Uganda, Rwanda, Tanzania and Kenya, and also occurs north of the Congo River where it is found north of Bangui, Central African Republic to southern Sudan in the east (see Sarmiento et al. 2001). It ranges between 400 and 2,500 m asl, mainly at elevations about 1,300 m in the eastern part of its range (Sarmiento et al. 2001).

Transitional forms are said to occur between whitesidei and katangae, katangae and ascanius, and katangae and atrinasus. There is a wide transitional zone between ascanius and atrinasus (Lernoud 1988; Sarmiento et al. 2001).