Circulating thyroglobulin antibodies (TgAb) and thyroperoxidase antibodies (TPOAb) were measured in 143 iodine-deficient children, 5 to 15 years of age, from the Region of Tula, Russia, who had been moderately contaminated after the Chernobyl disaster (37-185 GBq/km2 of caesium-137, [group A]) and in 40 sex- and age-matched subjects from an uncontaminated neighboring area (<3.7 GBq/km2 of caesium-137, [group B]). Increased thyroid size at sonography was found in 41% and in 45% subjects from group A and group B, respectively, associated with supranormal thyrotropin (TSH) values in 7.7% of group A and 7.5% of group B, without differences in average serum free thyroxine (FT4), free triiodothyronine (FT3) and TSH. Serum thyroperoxidase antibody (TPOAb)-associated or not with thyroglobulin-antibody (TgAb) as detected in 18.9% of children and adolescents from group A, about four-fold higher than in group B (5%, Fischer's exact test p<0.05). A 24% frequency was found in subjects whose age, at the moment of the disaster was 0-72 months or were in utero, but the frequency was about 7%, similar to that in group B, in those who had not yet been conceived at that time. Less than half of antibody-positive group A children were hyperthyrotropinemic, whereas no group B subclinical hypothyroid subject was antibody-positive, thus excluding the autoimmune etiology of the subclinical thyroid failure; more likely it is attributable to iodine malnutrition. The high prevalence of humoral thyroid autoimmunity phenomena in the investigated area suggests a combined role of iodine malnutrition in enhancing the effects of short lived iodine isotopes, particularly evident in pubertal individuals conceived or born immediately before the Chernobyl disaster.