Down Syndrome (DS) or trisomy 21 (T21) is the most frequent and the best known malformation syndrome associated with mental deficiency that appears in human,. Average incidence of this syndrome is about 1:700 newborns. Numerous researchers noted thyroid disorders in people with Down Syndrome but, clinical symptoms of thyroid dysfunction are difficult to separate from DS phenotype. The aim of this study was to examine the thyroid function in the patients with DS. Our results confirmed higher frequency of thyroid dysfunction in DS patients. Higher values of TSH were found in 60,34% of the examined DS patients, which is significantly higher value comparing with the control group (p<0,01). Compensated hypothyroidism was established in 27,92% of the examined DS patients, and most of those (63,23%) were younger than 6 years. The conclusions emphasize the necessity of implementation of thyroid function screening program in persons with DS, and the need for adequate treatment of its dysfunction. Thus, the symptoms of the disease would be alleviated and better physical and mental fitness ensured.