Iodine deficiency, the leading preventable cause of intellectual impairment in the world (World Health Organization, 1999), has reappeared in Australia. Recently, we identified the re-emergence of iodine deficiency in Sydney (Gunton, Hams, Fiegert & McElduff, 1999). This has been confirmed locally (Li, Ma, Boyages & Eastman, 2001) and interstate (Guttikonda et al., 2002), most recently in a study of Melbourne schoolchildren (McDonnell, Harris & Zacharin, 2003). We also provided evidence that iodine deficiency influences neonatal thyroid function (McElduff, McElduff, Gunton, Hams & Wiley, 2002). Evidence has been presented from other developed countries that iodine deficiency is re-emerging as a major potential health problem (Hollowell et al., 1998). The reasons for this are not clear, but a loss of awareness of the potential of iodine deficiency in the developed world and a decreased use of iodised salt appear to be major contributors (Gunton et al., 1999). Iodine deficiency impairs brain development through foetal hypothyroidism and in particular hypothyroidism in the early stages of pregnancy (Glinoer et al., 1992; Hetzel, 2000). Endemic cretinism, which is characterised by intellectual impairment, spastic diplegia and deafness, is due to severe iodine deficiency during pregnancy (Hetzel, Chavadej & Potter, 1988). It has been suggested that severe brain impairment easily identified as cretinism is merely one end of a continuous spectrum of neuro-psychological impairment induced by iodine deficiency (Boyages, 1994). Maternal iodine supplementation in populations with high levels of endemic cretinism results in a reduced incidence of cretinism without significant adverse effects (Mahomed & Gulmezoglu, 2000). In populations with less severe iodine deficiency and without cretinism the benefit of iodine supplementation is not as rigorously established, although a meta-analysis suggests an improvement in neuro-psychological functioning with iodine supplementation (Bleichrodf & Born, 1994). The average scores of cognitive capacity (a term used by the authors to amalgamate a variety of different intelligence tests) are improved by about 10% with iodine supplementation (Bleichrodf & Born, 1994).