The incidence of neural tube closure abnormalities, and particularly Spina-bifida is correlated with a low dietary intake of folic acid, for which the marker is the erythrocyte folate concentration. Initially, preventive policies concerned women treated with anticonvulsant agents and those with a known family history of Spina-bifida. This constituted secondary prevention. The objective of this study was to demonstrate the methods and respective role of secondary and primary prevention in 1998. The evolution away from secondary prevention towards primary prevention, i.e. aimed at all women who intend to conceive has been based upon the fundamental epidemiological estimate that 95% of cases of Spina-bifida occur in babies born to women without a known family history of this type of disorder. The idea that dietary measures alone may suffice to ensure effective prevention is invalid. However, if used in addition to a mean dietary intake of 200 micrograms folic acid a day, the only use of pharmacological or synthetic supplementation of 200 micrograms/day makes it possible to achieve the desired threshold of Dietary Folate Equivalents of 600 micrograms/day. The dose of 200 micrograms/day has been judged by the authors as being the most effective and safe for use on a large scale in the general population. Today, in 1998, the primary prevention of neural tube closure abnormalities is the subject of an international consensus which recommends folate supplementation of 100 to 200 micrograms/day during the periconceptional period. Implementation of this solution in the context of a health education campaign would meet the expectations of many women, in as much as 66% of them have declared that they would be ready to comply with such primary preventive measures.