Neural tube defects (open spina bifida, anencephaly, and encephalocele) represent the first congenital malformations to be preventable through public health measures such as supplementation and/or food fortification with folic acid. In Chile, starting in January 2000, the Chilean Ministry of Health legislated to add folic acid to wheat flour (2.2 mg/kg) to reduce the risk of NTDs. This policy resulted in an estimated mean additional supply of 427 microg/d in significant increases in serum folate and red cell folate of 3.8 and 2.4-fold, respectively, in women of fertile age, one year after fortification. The impact on the rate of NTDs is presently being studied in all births, both live births and still births, with birth weight >500 g in the city of Santiago. Preliminary results show a reduction of 40% in the rates on NTDs from the pre-fortification period (1999-2000) to post-fortification period (2001-June 2002). Fortification of wheat flour with folic acid in Chile is effective in preventing NTDs in Chile.