Asthma is the most common chronic disease in childhood. Over the past 30 years, prevalence of childhood asthma has increased several folds throughout the world. In Asia, such increase has been observed in series of studies from South Korea, Taiwan, Thailand and Singapore as had been observed in industrialized countries. Available epidemiologic studies in Asia indicated that allergen exposure is the major risk factor for the development of childhood asthma. House dust mites and cockroaches are the major allergens sensitized by asthmatic children in Asia. Despite increasing evidence to support the popular 'Hygiene Hypothesis' in explaining the increase of allergic diseases in Europe and USA, results from limited studies in Asia are quite controversial. It is established that prevalence of childhood asthma is low among those residing in mainland China as compared to those living in Hong Kong. Nevertheless, recent studies on BCG vaccination from Hong Kong and Thailand did not indicate any difference in prevalence of allergic disease between children with/without significant tuberculin reactions. Limited information on smoking and breastfeeding exists from the region. A study from Japan indicated that breastfeeding was found not to exert a protective effect for the development of childhood asthma. In environment with multiple ethnicities such as in Asia, there is a great opportunity for a collaborative research on epidemiology of childhood asthma. The success of which will bring about further understanding on pathogenesis of asthma and on the increasing prevalence of allergic diseases in this region.