As the production, distribution and consumption of iodized salt has increased in recent years, this study was carried out to assess iodine status in Tehran in 1996. 1146 families comprising 5140 subjects in the twenty districts of Tehran city from all age groups were randomly selected. Thyroid size was examined by palpation and graded according to the WHO classification. In 163 families selected randomly, thyroid size was determined by ultrasonography and urinary iodine was measured by digestion method. Serum T4, T3 and TSH (IRMA) concentrations were also assayed by kits. Percentage of grades 1 & 2 goiter were 44 & 44% in females and 49 & 33% in males respectively. Median urinary iodine was 17.5 micrograms/dl. Mean serum T4, T3 and TSH were 8.41 +/- 1.4 micrograms/dl, 170 +/- 37 ng/dl and 1.4 +/- 0.8 mu/ml, respectively. In 118 children aged 6-10 years median urinary iodine was 17.5 micrograms/dl. Thyroid volume in children was 4.3 +/- 1.9 ml. No correlation was established between the thyroid volume and goiter grade. This study points to the adequacy of iodine intake in the majority of families residing in Tehran.