Past studies relating smoking during pregnancy (and afterwards) and later child development are critically reviewed. There are consistent deficits among offspring of smokers in stature, cognitive development and educational achievement, as well as more frequent problems of temperament, adjustment, and behavior, particularly abnormally high levels of activity and inattention. The meaning of these relationships remains obscure, since it cannot be assumed that these abnormalities of child development are caused by parental cigarette smoking. In most studies there has been relatively little attention paid to the potential confounding by social, demographic, and psychological differences between smokers and nonsmokers. It is thus essential to carefully balance the comparative impact of social and environmental influences that may be different between families of smokers and nonsmokers, versus the toxic effects of tobacco.