The paper examines the relation of maternal smoking during pregnancy and lung function of 1029 schoolchildren aged 9 years. Children from Cracow whose mothers had smoked during pregnancy had significantly lower lung function than the children whose mothers had not smoked in this period. On average, spirometric data of FEV1/FVC, FEF25-75% and PEFR were 1.1%, 4.7%, and 3.2% lower respectively, in those children whose mothers had smoked during pregnancy. The effect was statistically significant after accounting for potential confounders such as current smoking habit of parents. The results provide a new support for the hypothesis that deficit in lung function among children is associated with maternal smoking in pregnancy. The strongest effects were found to involve the function of small airways.