Cigarette smoking is a well-know health hazard, probably not least for patients suffering from asthma. This review gives a short overview concerning the effects of passive and active smoking on the inception and outcome with regard to longitudinal changes in lung function and mortality for patients with asthma. Substantial evidence suggests that smoking affects asthma adversely. Exposure to environmental tobacco smoke in children, especially maternal smoking, may be a significant risk factor for asthma. Environmental tobacco exposure in patients with established asthma is not only associated with more severe symptoms, but also with lower quality of life, reduced lung function, and increased health care utilisation for asthma, including hospital admissions. Active smoking appears not to be a significant risk factor for asthma, but it is associated with worse outcome with regard to both longitudinal changes in lung function and asthma-related mortality. Based on the current knowledge, it therefore seems of utmost importance to encourage patients with asthma not to smoke. In line with this, patients with asthma should be given full support in their right to a smoke-free environment.