Objectives. To describe maternal exposure to tobacco in the three months before conception and throughout pregnancy, examine risk factors associated with tobacco exposure in pregnancy and smoking cessation, assess use of pharmacotherapy for smoking cessation and evaluate birth outcomes by smoking status. Design. A cohort of women from a multi-site United States study were asked retrospectively about their exposure to tobacco. Population. The study population was comprised of 4,667 mothers of non-malformed control infants who participated in the National Birth Defects Prevention Study from 1997 to 2003. Methods. Using computer-assisted telephone interview responses from this population-based sample, we assessed patterns of maternal smoking and exposure to environmental tobacco smoke (ETS) as well as use of pharmacotherapy for quitting smoking during pregnancy. Results. Overall, 961 (20.6%) mothers reported any smoking and 1,401 (30.0%) reported any exposure to ETS at home or work during the three months before conception through pregnancy. Of the 961 smokers, 512 (53.3%) reportedly quit smoking before or during pregnancy, including 379 (74% of quitters) in the first trimester, and 420 (43.7%) continued to smoke throughout the pregnancy. Only 2.1% of smokers reportedly used pharmacotherapy to quit smoking anytime from three months before conception through pregnancy. Low birthweight and preterm delivery rates were lowest among offspring of non-smokers and highest in offspring of those who continued to smoke throughout pregnancy. Conclusions. About one-half of mothers who reported preconceptional smoking quit before or during pregnancy. Use of pharmacotherapy to quit smoking during pregnancy was not common.