The evaluation criteria of the enlarged thyroid gland becomes a key problem when analyzing the prevalence of goiter in the population of school children. The review of the literature and own experience indicate lack of a consensus concerning this problem among researchers. Similarly, in the report of WHO in the year 2001 concerning the problem of iodine deficit and goiter endemia, experts did not present universal referential values of the thyroid size in ultrasonography for children population aged 6-15 years living in the regions of proper iodine supply in the diet, thus suggesting the necessity of working out regional norms.The aim of the study was to evaluate the prevalence of goiter in children aged 6-13 years from schools chosen randomly in Białystok with proper iodine supplementation in the study population and to estimate the usability of referential values applied in the assessment of the thyroid size.In the year 2002, the examination was carried out in 4 elementary schools chosen randomly from Białystok. A total of 480 children aged 6-13 years were included in the study. All children were examined physically with palpation assessment of the thyroid size and had USG of the thyroid. The concentration of iodine was measured in the morning urine. The blood samples were collected to determine hTSH concentration.In palpation, with regard to WHO criteria of the year 2001, the prevalence of goiter was 6.8% in the study population. Applying WHO criteria of 1994 in palpation assessment of goiter increased this percentage up to 18.2%. When using WHO criteria for body surface of 1997 to evaluate goiter by USG, its percentage equaled 7%, whereas taking into consideration referential values for child's age doubled its percentage up to 13.5%. The percentage of goiter increased up to 45.5%, when referential values introduced by Gutekunst et al. were applied.When evaluating the thyroid size in ultrasonographic diagnostics of goiter in children aged 6-13 years, it seems more purposeful to apply referential values of the thyroid size regarding the body surface and sex (manifesting a child's actual physical development) than to use the norms concerning the calendar age. The prevalence of goiter amounting 7% in the population of school children in spite of adequate iodine prophylaxis suggests other than iodine deficit, factors causing goiter in this population.