Chromosome counts and karyotype data are presented for three species and two subspecies of the Hominoidea and two species of gibbon (Hylobates). The results are compared with the human chromosome set. Pongo pygmaeus (the orangutan), Gorilla gorilla gorilla and Gorilla gorilla beringei (the lowland and mountain gorillas); Pan troglodytes troglodytes and Pan troglodytes paniscus (the northern and pygmy chimpanzees) all have 48 chromosomes while man (Homo sapiens) has 46. The karyotypes differ most widely in the relative number of long acrocentric and metacentric chromosomes. Hylobates lar (Lar gibbon) and Hylobates moloch (Sunda Island gibbon) have 44 chromosomes all of which are metacentric. These findings support the suggestion that the African great apes (Gorilla and Pan) are more closely related to man than the Asiatic apes (Pongo and Hylobates). It can be further suggested on the grounds of karyotype morphology that the gibbons (Hylobates and Symphalangus) should be classified in a separate family placed perhaps either in the Cercopithecoidea or Hominoidea.