The results of study concerning iodine deficiency among children attending primary schools in Warsaw and Ciechanów voivodships have been presented. The study was a part of a nationwide program on iodine prophylactics and incidence of goiter in Poland. Altogether 675 children, 356 girls and 319 boys of age between 6 and 13 years, were included into the study. Of these, 337 inhibited urban, and 338 rural areas. The presence of goiter was found in 48.6% of the studied population. In 60% of the affected children the degree of thyroid enlargement was small (IB). The incidence of goiter was higher in rural than in urban children and higher in girls than in boys. In above 90% goiter was of the diffuse type. In almost 65% of cases the diagnosis of goiter by palpation was confirmed by ultrasonography. The urinary concentration of iodine was low in 85% of the children studied. This was true for 88% of children with goiter and for 83% of children with normal size of the thyroid. Only 12% of the children studied used iodinated salt in the diet. The use of iodinated salt was more popular among urban children than among the rural ones. Low urinary concentration of iodine was found both in children not consuming and in the majority of those consuming iodinated salt. The individual iodine prophylactics had no effect on the incidence of goiter. The results obtained indicate the presence of iodine deficiency in the studied region suggesting urgent need for informative action explaining the existing situation and necessity of undertaking the widespread and effective prophylactic measures.