The increasing prevalence of childhood asthma in the developed world is a cause for concern. A so-called Western lifestyle has been the factor most commonly cited to explain this worrying increase in asthma prevalence. Early studies in a limited number of African countries showed a very low rural prevalence of childhood asthma, especially where children lived according to a traditional lifestyle. These same studies showed that asthma was not uncommon in urbanized African children. There has been an increasing tendency over the past 20 years for those in rural communities to move to the large urban centers. This article analyses the urban-rural differences and factors that influence the development of asthma in susceptible children.