Cigarette smoking during pregnancy has been causally associated with an increased risk of both intrauterine growth retardation and preterm delivery but most strongly with low birth weight. No such study to date had ever dealt with the Cypriot population. In interviews with their gynaecologists 65,530 pregnant women were asked between January 1990 and August 1996 to answer two questions, whether they had been smoking before and whether they had been smoking during pregnancy. Data from 59,014 births were considered to have valid birth weight data for this investigation. In 81.2% of the cases the mother explicitly declared that she had neither smoked before or during pregnancy whereas in 1.4% of the cases the mother said that she had smoked both before and during pregnancy and in 1.4% of the cases the mother said that she had smoked before but not during pregnancy. Finally, in 15.3% of the cases no answer to "smoking question" was given, whereas in 0.7% of the cases the answer that was given was deemed as not clear. The average birth weight of babies born to women who had stopped smoking was insignificantly different than that of those born to never smokers. The average birth weight of babies born to women who smoked during pregnancy was lower compared to babies born to non smokers' babies by 92 grams, 66 grams, and 109 grams for all babies, singleton boys and singleton girls respectively. The greatest effect to their mean birth weights was observed in babies whose mothers did not answer the question on smoking. Their babies had birth weights lower than non smokers' babies by 203 grams, 197 grams, and 201 grams for all babies, singleton boys and singleton girls respectively.