Environmental tobacco smoke and constituents are global risks for human health. Considerable evidence shows that environmental tobacco smoke exposure contributes to, and exacerbates, respiratory disorders. This review assesses the causal role of environmental tobacco smoke exposure for childhood respiratory disorders, and in particular asthma. Tobacco smoke and environmental tobacco smoke exposure during pregnancy have an effect upon lung function in newborn infants; exposure after birth also has an effect upon lung function. An effect upon bronchial responsiveness has been suggested but the evidence is not as strong as for lung function. From 1997 to 1999 a comprehensive set of systematic reviews concerning the relationship between exposure to environmental tobacco smoke and respiratory health in children summarized the results from hundreds of published papers. The evidence for a causal relationship between environmental tobacco smoke exposure and asthmatic symptoms on the one hand, and between environmental tobacco smoke exposure and reduction in lung function on the other hand, was quite strong, whereas the evidence between environmental tobacco smoke exposure and development of allergy was much weaker. Here we present an overview of the effects of environmental tobacco smoke exposure on lung health in children. A hypothesis has been put forward regarding upregulation of pulmonary neuroendocrine cells in relationship to mechanisms of tobacco smoke products (TSP)-induced pulmonary disease. It has also been reported that genetic variation makes part of the population especially vulnerable to environmental tobacco smoke exposure during pregnancy. Furthermore, there is a need for intervention to reduce environmental tobacco smoke exposure in young children, by educating parents and adolescents about the health effects of environmental tobacco smoke exposure. Studies are needed to identify possible critical periods when environmental tobacco smoke exposure is more likely to induce harmful effects on lung health in young children in order to implement effective preventive strategies.