OBJECTIVE: Multinodular goitre has been found with a high prevalence in iodine-deficient areas, but less frequently in iodine-replete areas; the iodine intake sufficient to prevent goitre has not been established, however. METHODS: We report data from an ultrasonic investigation of the thyroid glands of 2656 randomly selected subjects aged 41 to 71 years in an area with borderline iodine deficiency. RESULTS: Median iodine concentration in spot urine samples was 70microg/l. Multinodular thyroid structure was found in 23% of the population, increasing in women from 20 to 46% with increasing age, and in men from 7 to 23%. Solitary, scintigraphically cold, thyroid nodules >10mm were found in 2.4% of the population with the same prevalence in the different age and sex groups. Two years of follow-up of these cold nodules revealed no signs of malignancies. Median thyroid volume was 11.0ml. Thyroid enlargement (>18ml for women and >25ml for men) was found among 13. 1% of the women and 6.2% of the men, and the prevalence increased with age. The presence of thyroid nodules was related to positive anti-thyroperoxidase antibody (TPO Ab) titres, whereas thyroid enlargement was associated with iodine excretion <50microg/day. CONCLUSIONS: Thyroid enlargement was associated with low iodine excretion and median thyroid volume was slightly increased compared with iodine-replete areas. Multinodular thyroid structure was found with a high prevalence and was associated with TPO Ab >200kU/l. Cold thyroid nodules were moderately prevalent, with no cases of detected malignancies during 2 years of follow-up.