The potto Perodicticus potto is a small, arboreal, nocturnal primate with an extensive, but poorly-known, distribution through tropical Africa, and a debated taxonomy. This paper (1) examines the Eastern Rift Valley as a major barrier to primate distribution in eastern Africa, (2) reviews the taxonomy of P. potto, (3) describes the distribution of the eastern potto P.p. ibeanus, (4) summarizes what is known about the body size, abundance, elevation and rainfall limits of P.p. ibeanus, (5) provides evidence for the presence of P. potto east of the Eastern Rift Valley, and (6) describes, names, and discusses a new subspecies of Perodicticus for Mount Kenya (the ‘Mount Kenya potto’ Perodicticus potto stockleyi). The geographic range for P.p. ibeanus is ca. 850 000 km² and extends from western Democratic Republic of Congo to western Kenya. P.p. ibeanus occurs where the mean annual rainfall is between 1300–2000 mm, and is not known to be present below 600 m or above 2300 m. Densities range from <2–28 individuals/km². P.p. stockleyi is described from one specimen that is phenotypically distinct from P.p. ibeanus and that derives from a population that is probably isolated from the nearest population of P.p. ibeanus by >175 km.