Neural tube defects (NTDs) are common fetal malformations. They are multifactorial in origin, with folic acid as the primary known environmental factor. It is recommended that all women consume 0.4 mg of synthetic folic acid daily if there is any possibility of becoming pregnant. Women who have had a previous pregnancy affected by NTD should increase their folic acid intake to 4.0 mg daily periconceptually. The purpose of this article is to review the relationship between folic acid and NTDs. It also discusses how the knowledge and use of folic acid has affected the incidence of NTDs, and ways in which the knowledge and use of folic acid before pregnancy can be increased.