Backgroud Iodine deficiency is the main cause for potentially preventable mental retardation in childhood and is still prevalent in large parts of the world. Objectives To assess the effects of iodised salt in comparison with other forms of iodine supplementation or placebo in the prevention of iodine deficiency disorders.Search strategy We searched the Cochrane Library, Medline, the Register of Chinese trials developed by the Chinese Cochrane Centre, and the Chinese Med Database. We performed handsearching of a number of journals (Chinese Journal of Control of Endemic Diseases, Chinese Journal of Epidemiology, Chinese Journal of Preventive Medicine, and Studies of Trace Elements and Health up to February 2001), and searched reference lists, databases of ongoing trials and the Internet. Date of latest search: November 2001. Selection Criteria We included prospective controlled studies of iodised salt versus other forms of iodine supplementation or placebo in people living in areas of iodine deficiency. Studies reported mainly goitre rates and urinary iodine excretion as outcome measures. Data collection amp; analysis As the studies identified were not sufficiently similar and not of sufficient quality, we did not do a meta-analysis but summarised the data in a narrative format. Main results We found six prospective controlled trials relating to our question. Four of these were described as randomised controlled trials, one was a prospective trial that did not specify allocation to comparison groups, and one was a large population-based study comparing different interventions. Comparison interventions included non-iodised salt, iodised water, iodised oil, iodation with potassium iodide versus potassium iodate. Numbers of participants in the trials ranged from 35 to 334; over 20 000 people were included in the population-based study. There was a tendency towards goitre reduction with iodised salt, although this was not significant in all studies. There was aim an improved iodine status in most studies (except in small children in one of the studies), although urinary iodine excretion did not always reach the levels recommended by the WHO. Reviewers’ conclusions The results suggest that iodised salt is an effective and safe means of improving iodine status. However, high quality controlled studies are needed to address questions of dosage and best means of iodine supplementation in different population groups.