Iodine is among the body's essential trace elements. While a deficiency in iodine is both easy and inexpensive to prevent, IDD (iodine deficiency disorders) nevertheless continue to be a significant public health problem in 118 countries. An estimated 1571 million people live in iodine-deficient environments. A large proportion of the severely deficient are women in their reproductive years whose babies are at high risk of irreversible mental retardation unless they receive adequate amounts of iodine. Iodine deficiency not only causes goitre; it may also result in irreversible brain damage in the fetus and infant, and retarded psychomotor development in the child. It is the most common cause of *preventable* mental retardation. It also affects reproductive functions and impedes children's learning ability. Current estimates of daily iodine intakes in Canada and the USA, where IDD is no longer a public health problem, are substantially above physiological need--in the range of 460 microgrammes/day among 9-16-year-old children, to greater than 1 mg among as many as 10-20% of adults. A generally accepted desirable adult intake is 100-300 microgrammes/day. WHO recommends iodized salt for iodine supplementation to correct iodine deficiency. Iodized oil is the preferred interim measure in areas of moderate or severe deficiency that will not be soon be covered by iodized salt. More information is available from: Dr Barbara Underwood, Nutrition unit, WHO, 1211 Geneva 27, Switzerland, e-mail: [log in to unmask] Jim Akre, Nutrition unit, WHO