In order to describe smoking habits among pregnant women and predictors of smoking cessation all pregnant women attending routine antenatal care from 1989 to 1991 at the Department of Obstetrics, Aarhus University Hospital, were asked to fill in questionnaires. Information about smoking habits from 8806 women revealed that 44% smoked prior to pregnancy. One fifth of the smokers stopped smoking early in pregnancy, leaving 33% women smoking during pregnancy. The strongest predictor of smoking cessation was the number of cigarettes smoked prior to pregnancy, where those that smoked the least were most likely to give up smoking. Caffeine intake, parity, years of education, and partner's smoking habits were also associated with smoking cessation whereas social status, alcohol intake, marital status, and age of the women had no influence on smoking cessation. Thus, a strategy for a smoking cessation campaign among pregnant women could be directed towards women who smoke heavily prior to pregnancy and women with a high daily intake of caffeine.