BACKGROUND:Use of periconceptional folic acid supplementation has been promoted in Western Australia since late 1992, and voluntary fortification of some foods with folic acid has been permitted in Australia since 1996. Reduced rates of neural tube defects (NTDs) have been observed since 1995. Aboriginal infants have a higher rate of NTDs, but no fall in rates has been documented. Encephaloceles have not been examined separately.METHODS:Data on anencephaly, spina bifida, and encephalocele were obtained from the Western Australian Birth Defects Registry. The prevalence ratio for each type of NTD was calculated, comparing 1993 to 1995 (promotion of supplements, no fortification) and 1996 to 2006 (promotion of supplements and voluntary fortification) with 1980 to 1992 (no promotion or fortification).RESULTS:From 1996 to 2006, there was a 32% reduction in anencephaly, 23% in spina bifida, and 34% in encephalocele compared with 1980 to 1992. There were no differences seen from 1993 to 1995 compared with 1980 to 1992. For Aboriginal infants, the rates were higher than for non-Aboriginal infants, for each type of NTD. The prevalence ratios, comparing 1996 to 2006 with 1980 to 1995, were 0.70 (CI, 0.61–0.79) for non-Aboriginal infants and 0.90 (CI, 0.61–1.32) for Aboriginal infants.CONCLUSIONS:Overall, the rates of encephalocele, anencephaly, and spina bifida have fallen to a similar extent in association with promotion of folic acid supplements and voluntary fortification. No such falls were seen for Aboriginal infants. These data will provide a useful baseline against which to monitor the effects of mandatory fortification on NTDs when it is introduced in Australia in September 2009. Birth Defects Research (Part A), 2009.