Chromosome counts and karyotype data are presented for five primates Tupaiaglis (Common tree shrew) has 62 chromosomes, 12 metacentric and 48 acrocentric autosomes, a metacentric X and acrocentric Y. Nycticehus coucang (Slow loris) has 5·chromosomes all of which including the X and Y, are metacentric. Tarsius bancanus (Horsfield’s tarsier) has 80 chromosomes, the highest number recorded for any mammal, 14 are metacentric and 66 are acrocentric. Since only a female could be studied the sex chromosomes were not identified. Cercocebus aterrimus (Black mangabey) has 42 chromosomes of which all, including the X and Y, are metacentric. Symphalangus syndactylus (Siamang) has 50 chromosomes of which 48, including the X and Y are metacentric and 2 are acrocentric. The karyotype of this species is compared with that of Hylobates lar (White-handed gibbon). These findings support the trend observed by others that within an order species with high chromosome numbers have many acrocentrics and those with low numbers have more metacentrics. This suggests that structural rearrangements may have played a large role in evolution. Whether more “specialized” forms have primarily acrocentric chromosomes and “generalized” forms less is discussed. It is concluded that more data is required to verify both of these hypotheses.