Certain uncommon genetic disorders occur relatively frequently in the various population groups of Southern Africa. Prominent among these are porphyria, colonic polyposis and sclerosteosis in the Afrikaner community, Huntington's chorea in the British, Gaucher's and Tay-Sachs diseases in the Jewish population, glucose-6-phosphate dehydrogenase deficiency (G-6-PD deficiency) and thalassaemia in the Greek community, various skeletal dysplasias in the Black group, lipoid proteinosis and cleidocranial dysostosis in the Cape Coloured population, diabetes mellitus in the Indian community and retinitis pigmentosa in the Tristan da Cunha islanders. In addition, 'private' syndromes have been encountered in virtually every group. Awareness of the ethnic distribution of unusual genetic conditions is of considerable practical importance during the differential diagnosis of obscure disease.