It has been reported that there is an increased risk of thyroid disorders associated with trisomy 21. The aim of this study was to investigate the thyroid function in 84 patients with Down syndrome. The ages of the patients were between 2 and 14 years. FT3, FT4, T3, T4, TSH, anti-T and anti-M antibodies were measured in all patients. TRH tests were applied to five patients with latent hypothyroidism. Ten patients (11.9%) with latent hypothyroidism, two patients (2.3%) with marked hypothyroidism, two patients (2.3%) with autoimmune thyroiditis and one patient with hyperthyroidism were diagnosed in this group of patients with Down syndrome. One of the two patients with autoimmune thyroiditis had normal levels of thyroid hormones while the other was hypothyroidic. The patient with hyperthyroidism presented all clinical and laboratory findings of hyperthyroidism. A careful investigation of thyroid disorders in patients with Down syndrome is recommended in order to ensure an early treatment program that will enhance their quality of life.