The aim of the study was to analyze data related to chronic autoimmune thyroid disease at diagnosis and at follow-up of children and adolescents in Lower Silesia in the years 1999-2004. Age, gender, incidence of thyroid disease in the family, clinical presentation, hormonal findings, levels of thyroid antibodies, results of ultrasonography, and fine needle aspiration biopsy (FNAB) were recorded. 100 children, 10 boys and 90 girls, were included in the analysis. The mean age at diagnosis was 12.3+/-2.3 years and at last examination 14.9+/-1.9 years. At diagnosis, increased levels of TSH without overt hypothyroidism was observed in 26 children. In 11 children hyperthyroidism was detected whereas 63 children were euthyroid. An increased level of thyroid peroxidase antibodies was observed in 65% of the children. Ultrasonography was characteristic for Hashimoto's thyroiditis in all patients. Fine needle biopsy was performed when there were diagnostic difficulties (35% children). Thus, in all the children the diagnosis of Hashimoto's thyroiditis was ascertained either by high antibody titer or FNAB. Associated diseases were observed in 33% of the children. Thyroid disease in the family was present in 25% of the children. There was a gradual decline in the number of new cases presented from 1999 to 2004. The reason for this decline remains speculative.