There is a strong relationship between male and female circumcision in traditional thought and, north of the equator, in their practice by ethnic groups. The Southwest Nigeria Study, a 1994-95 survey of 1749 males and 1976 females in Nigeria's Ondo, Oyo and Lagos States, is used to examine contemporary levels of circumcision, reasons for carrying out the practice, and the circumstances of the circumcision operations. These findings are compared with earlier southwest Nigerian and West African studies. The persistence of the practices is confirmed, but rapid change towards their medicalization is also established. Possible links with AIDS are discussed.