Cigarette smoking remains a frequent problem during pregnancy. Nicotine has deleterious effects on the foetus. The most common problem remains "small for date" babies. However, this is a minor problem compared with two major toxic consequences: intellectual impairment and increased rate of infantile cancer. Many studies have shown diminished intellectual capacity, behavioural problems and an increase of sudden infant death syndrome. The cancerigenic and genotoxic effects of smoking are well documented with recent studies showing the genotoxicity of amniotic fluid in smoking pregnant women and lymphocyte chromosome mutation in newborns. The frequency of cancers, particularly leukaemia, lymphoma and cerebral tumours are increased in children born to women who smoke during pregnancy. It is therefore excessively important to help pregnant women and their doctors become aware of the toxic effects of active or passive smoking in pregnancy and encourage the patients and their friends and relations to stop smoking as soon as pregnancy is diagnosed or if it's possible before the pregnancy.