Although a great deal is known about the incidence of cancer, including oral cancer, no such study has been done on odontogenic tumors and jaw cysts. There are therefore no standardized data which would allow for comparative incidences in different countries and between different groups. In the present study, cases of ameloblastomas and dentigerous cysts derived from the records of all the hospital pathology departments and private pathology practices on the Witwatersrand, were recorded for the 10-year period 1965--1974. The population at risk (1970 census) was 974,390 Whites and 1,567,280 Blacks. The annual incidence rates, standardized against the standard world population, for ameloblastomas per million population are 1.96, 1.20, 0.18 and 0.44 for Black males, females and White males, females, respectively. The equivalent four figures for dentigerous cysts are 1.18, 1.22, 9.92 and 7.26. These figures show that ameloblastoma is very much more common in Blacks than Whites in the population at risk. Conversely, dentigerous cysts are much more common in Whites. This makes it unlikely that dentigerous cysts predispose to ameloblastoma formation. These epidemiologic observations give rise to speculation as to whether some component of the South African Black diet or other environmental substance might possibly be an etiologic factor in ameloblastoma.