Revising the grey-cheeked mangabeys (Lophocebus albigena group) in the light of the Phylogenetic Species Concept reveals more taxonomic diversity than was formerly suspected. The three subspecies recognized by Groves (1978) are diagnosably distinct, and are here upgraded to species rank. Most significantly, the mangabeys of Uganda, not recognized as distinct at all in the 1978 revision, are now shown to constitute a fourth species, Lophocebus ugandae (Matschie, 1912), which is apparently confined to Uganda, and as such probably Uganda's only endemic primate