Duplication of segments within the MHC has led to numerous multicopy families such as class I, class II, C4 and MIC (PERB11). Different copy numbers between haplotypes and species may be explained by the extent of duplication and subsequent deletion. There are at least five copies of MIC (PERB11) in humans, but MICA (PERB11.1) appears to have been deleted from the chimpanzee.By comparing the sequences of primates (chimpanzee, gorilla, gibbon, orang-utan, pygmy chimpanzee, Patas monkey, Aethiops and baboon) we conclude that the gorilla has a copy of PERB11.1, whereas the baboon and Patas possess MICD (PERB11.4) and/or MICE (PERB11.5 rather than MICA. (PERB11.1). These findings indicate that the primate MHC is more plastic than has been appreciated.