Up-to-date observations in the regions where effective food iodine supplementation was introduced confirm a significant decrease in goiter incidence. However, in some regions the incidence of goiter remains unchanged or even the increase in the frequency of autoimmunological diseases of the thyroid like, Grave's-Basedov disease and chronic/subacute lymphocytic thyroiditis is observed. The purpose of the study was to evaluate the prevalence of autoimmunological diseases of the thyroid in children aged 6-13 years in the Polish population after 5 years of obligatory iodine supplementation program. The study included 480 school children from 4 elementary schools chosen randomly in the city of Białystok and 120 patients at the same age treated due to goiter with KI and/or thyroxin for minimum 12 months in the Regional Specialist Outpatient Clinic of Endocrinology. All children underwent physical examination with palpation of goiter and USG of the thyroid. Iodine concentration was assessed in the morning urine by the catalytic method of Sandell-Költhoff. The concentrations ofTSH and antibodies against TSH, thyroid-peroxidase (TPO) and thyroglobulin (Tg) were also determined. The mean concentrations of anti-Tg antibodies were statistically significantly higher in children with goiter in comparison with children with the thyroid gland within the norm (155.8 IU/ml vs. 24.4 IU/ml, p = 0.045). In children with goiter the incidence of'positive' titre of anti-Tg antibodies was 4-fold as high as in children without goiter (33.3% vs. 8.7%, p = 0.0147). High incidence of antibodies against thyroglobulin in the population of children with goiter and a positive correlation between the titre of anti-Tg antibodies and the size of the thyroid in this group suggest a significant role of autoimmunological disorders in the pathogenesis of goiter in the studied population.