Smoking during pregnancy has in many countries replaced poverty as the most important preventable risk factor for an unsuccessful pregnancy outcome. Maternal smoking induces fetal hypoxia and morphological changes in the placenta, which increase the risks of intrauterine growth retardation and placental abruption, which may cause late fetal death and possibly also neonatal mortality. Smoking influences post-neonatal mortality through increased risk of sudden infant death syndrome (SIDS), but why maternal smoking increases the risk of SIDS is essentially unknown. In reducing the overall smoking prevalence in society, general preventive measures have been successful. Such measures, which aim at preventing young girls from starting to smoke are in the long run the most effective way to reduce smoking during pregnancy.