SLE has a high prevalence in Afro-Caribbean populations but has been reported to be rare in west Africa. We assessed prevalence (per 100000) of SLE in women in an area of south London and estimated it to be 177 (95% CI 135-220) in Afro-Caribbeans, 110 (58-163) in west Africans, and 35 (26-43) in Europeans. The high prevalence of SLE in recent migrants from west Africa suggests that the disease is not rare in west Africa, and that there is a genetic basis for the high risk of SLE in people of west African descent compared with other groups.