Maternal smoking during pregnancy is associated with a number of psychological problems in offspring including depression but it is not clear whether this is due to intrauterine exposure to tobacco smoke or due to other lifestyle (confounding) factors. This project will compare associations of maternal smoking during pregnancy to those of paternal smoking during pregnancy with offspring depression measured at 18 years. Maternal and paternal smoking during pregnancy should be similarly associated with lifestyle and demographic factors. However, paternal smoking during pregnancy will expose the foetus to much lower levels of tobacco exposure than active smoking by the mother. Therefore if there is an intrauterine effect on depression, we would expect to see much stronger associations with maternal smoking than with paternal smoking.