There is an urgent need for epidemiological assessments of environmental factors associated with rapid urbanisation in developing countries. Unlike the process in developed countries, urbanisation in the developing world is often associated with urban poverty, particularly on the periphery of the city where informal settlement areas develop. Population growth rates in these areas are frequently higher than in the city itself, and access to basic environmental amenities is frequently lacking. In Africa, ill-health conditions associated with rapid urbanisation, such as diarrhoea and acute respiratory infections, continue to be major causes of childhood deaths. An account is given of research being conducted in South Africa to address such problems, as well as problems related to inner-city decay, such as childhood lead exposure. There is a critical need for better inter-sectoral co-ordination between the health sector and other sectors such as housing and planning, in preventing negative health impacts associated with rapid urbanisation in the future.