Neural tube defects (NTDs) involve incomplete development of the embryonic structure that becomes the brain and spinal cord. They affect about 4,000 pregnancies a year and thus are among the most common of severe birth defects. Spina bifida and anencephaly account for 90% of them. Their incidence is dropping, however, because of the use of folic acid dietary supplements to prevent these defects. Prenatal diagnosis could now detect 70% of NTDs, but the tests produce many false positives, so the question is under what circumstances should they be recommended to pregnant women. This text provides authoritative discussions of a wide range of theoretical, experimental and clinical issues, and is divided into sections on embryology, clinical features, epidemiology, genetics, treatment and patient education, and public health.