There are wide variations between countries in the prevalence of asthma-related symptoms. The differences in Europe are striking, with higher rates in the United Kingdom and Ireland and lower rates in southern and eastern Europe. However, comparisons between countries require more information on incidence and prevalence trends in Europe. Such comparisons would serve to generate hypotheses regarding the main risk factors involved and would guide public health policy to respond to this major threat. More surveillance of asthma incidence and prevalence is therefore needed. On the basis of sound research, public health interventions are needed to prevent the onset and exacerbation of asthma in children; environmental policies, such as the determination of air quality standards, should take account of the impact of air pollutants on children's health.