Smoking is one of the most important preventable public health problems. Prevalence of smoking is decreasing in the Western world but lot of work is left. We reviewed the most important papers related to smoking and asthma. Despite of decreasing smoking figures in Finland, about 15-20 per cent of pregnant women smokes. Children's exposure to harmful effects of environmental tobacco smoke (ETS) still continues. Exposure to tobacco smoke during pregnancy and in early childhood both deteriorates permanently children's lungs and increases their asthma risk. The exposure of adults to ETS also increases their asthma risk. Both passive exposure to ETS and active smoking worsen asthma. In addition, smoking asthmatics run a higher risk of developing COPD compared to non-smokers. Smoking prevalence among the population can be regulated through legislation, but the health care personnel have a central role in encouraging smoking cessation among smoking patients.