The role of folic acid and homocysteine in pregnancy is becoming clearer. The efforts of many countries to prevent neural tube defects through public awareness of folic acid have been disappointing, but evidence is now emerging that the food fortification programs in the United States and Canada are effective in reducing the numbers of neural tube defects, and there may be additional benefits in terms of other congenital defects such as oral-facial clefts and congenital heart disease. Homocysteine has a significant association with vascular disease in later life, is elevated in preeclampsia, and has been associated with other pregnancy complications such as early pregnancy loss. The data from cohorts of women with a history of preeclampsia during pregnancy indicate that they are at increased risk for cardiovascular and cerebrovascular disease in later life. Elevated homocysteine concentrations may be a common link that accounts for these associations.