Abstract. The availability of iodinated salt containing 20 mg of iodine as iodate/kg salt consumed on a voluntary basis enabled us to investigate its effect on goitre prevalence and iodine excretion in urine in a longitudinal, prospective, randomized study over 4 years. With this salt, under the assumption of a consumption of 5 g salt per day and person, an additional intake of 100 μg of iodine can be achieved. The study was performed on initially 334 children (168 boys, 166 girls) at the age of 10 years living in an area of iodine deficiency. After 4 years, 286 children still participated in the study. Initially, goitre prevalence as assessed by palpation was found to be 30.5% (37.4% in girls and 23.8% in boys). Neck circumference was found to be significantly higher in children with goitre compared with those without (30.2 ± 1.4 vs 29.4 ± 1.4 cm; P < 0.001). Iodine excretion in the urine was significantly lower in children with goitre compared with those without (40.4 ± 16.7 μg/g creatinine vs 46.1 ± 24.9 μg/g creatinine; x ± sd; P < 0.05). The children were randomly assigned to two different groups: group A (N = 146) was asked to use iodinated salt, group B (N = 188) non-iodinated salt. Over the 4 years, a continuous increase in iodine excretion in urine could be demonstrated in group A. After 1 year, it was significantly higher than in the control group that used non-iodinated salt. After 4 years, the mean iodine excretion in children using iodinated salt was 60.1 ± 24.1 μg/g creatinine in contrast to 45.1 ± 18.6 μg/g in the control group (x ± sd; P< 0.0001). However, no decrease in goitre prevalence could be documented: after 4 years, 23.8% of the children belonging to the group using iodinated salt and 22.5% of those in the group taking non-iodinated salt had a goitre. From these observations we conclude: 1. The voluntary use of a commercially available iodinated salt containing 20 mg iodate/kg leads to a significant increase in iodine intake, measured by urinary iodine excretion. Even after 4 years, the value is far below the daily iodine intake recommended by the WHO. No decrease in goitre frequency could be assessed. 2. An increase in iodine ingestion can be achieved either by increasing the iodine content of the salt or by application of iodine by alternative measures. The safest way would be to use iodinated salt exclusively, i.e. also in the food industry and restaurants. An increase in the iodine content of the salt and its continuous voluntary use would lead to a large variation in iodine intake. A higher risk of adverse reaction, e.g. iodine-induced thyrotoxicosis, cannot be excluded in susceptible persons.