It was attempted to assess the incidence of thyroid diseases in Polish children born between 1980-1986, who at the time of the Chernobyl nuclear disaster were 0-6 years old, or whose mothers were in the third trimester of pregnancy. 3071 children have been examined, 1772 girls and 1299 boys. The following were assessed in each child: the health status, the developmental level, the thyroid ultrasound examination, and the level of TSH, FT4, antithyroid antibodies ATM and ATGL in the blood serum. Disorders in thyroid morphology (abnormal echogenicity) have been found in 462 children (15%), almost twice as much in girls than in boys. Goiter has been recognized in 4.6% of all children, an abnormal echogenity in 5.4% and focal changes in 4.8%. 3.9% of children have been found to have a high level of ATM antibodies, and 8.7%--a high level of ATGL antibodies. Among 6 children, who had thyroidectomy, 2 children have been diagnosed to have ca papillary and 4 children--adenoma.