HLA-B27 is present throughout Eurasia but is virtually absent among the genetically unmixed native populations of South America, Australia, and among equatorial and southern African Bantus and Sans (Bushmen). It has a very high prevalence among the native peoples of the circumpolar arctic and subarctic regions of Eurasia and North America, and in some regions of Melanesia. Results of recent epidemiologic studies of spondyloarthropathies in populations with a relatively high prevalence of B27 are also reviewed.