The studies concerning iodine deficiency and occurrence of goiter, being a fragment of the program covering different parts of Poland, included 2620 children of age between 7 and 12 years attending randomly chosen schools situated in towns and villages of Poznań, Pila, Leszno, Konin, Kalisz, Bydgoszcz and Zielona Góra districts. Among the children studied, 1009 children (522 boys and 487 girls) attended town schools, and 1611 (774 boys and 837 girls) country schools. All children were subjected to anamnesis by using a standard questionnaire. Also physical examination of the thyroid aimed at the evaluation of size and morphology of the gland was carried out by palpation (according to the obligatory WHO scale) and by ultrasonography. Urine samples were taken from the majority of children for the determination of urinary excretion of iodine. In 736 (28.1%) of the studied children an enlargement of the thyroid was found. Among these children 253 are inhabitants of towns (this number represents 27.8% of all urban children studied) and 483 are inhabitants of villages (30% of all rural children studied). In 92.7% of cases the goiter could be classified as type IB according to WHO and in 56 cases it was of nodular character. There was a clear relation between the incidence of goiter and the age of the children studied. Frequency distribution of goiter in the individual age groups was as follows: for urban children--21.8% in age group of 7-8 years, 23.5% in age group of 9-10 years and 29.7% in age group 11-12 years, and for rural children the corresponding values were 21.1%, 30.2% and 38.2%. Mean urinary iodine excretion was 96 micrograms/L (median 84 micrograms/L) for urban children, and 87 micrograms/L (median 64 micrograms/L) for rural children. Among 2620 answers concerning the use of iodized salt in the household, only 980 (37.1%) were positive. In towns, the use of iodized salt declared about 41% of families and in villages about 35%. Altogether, among 736 cases of goiter, 464 are children not using iodized salt. Only in 272 cases goiter appeared despite the use of iodized salt. The data concerning family occurrence of goiter and the type of iodized salt used can be treated as approximate because of subjective character. According to the results obtained, the region covered by the study falls according to the WHO and ICCIDD classification to the category of an area of mild iodine deficiency requiring more intensive iodine prophylaxis.