Spina bifida and anencephaly, the common form of neural tube defects, affect approximately 300 000 newborns each year worldwide. The effectiveness of folic acid supplementation in preventing their occurrence or recurrence has been unambiguous since 1991. In general, the prevalence of these abnormalities has decreased in the past 20 to 30 years because of periconceptional folate supplementation, food fortification in several countries, avoiding exposure to environmental factors, and increased accuracy of prenatal screening for fetal anomalies. Women who are planning to conceive should be informed about the importance of folic acid in fetal development and advised to take 400 µg/day of folic acid supplements. Food fortification with folic acid will ultimately be necessary to reduce the number of patients. Primary prevention of neural tube defects by the periconceptional intake of folic acid is a major public health opportunity and has wide implications in reducing the mortality and morbidity of offspring.