Resistance to thyroid hormones (RTH) is a rare disease with prevalence 1 : 40 000-50 000. About 85% of cases are caused by mutation of thyroid hormone receptor gene β (TRβ) and in 15% of cases the mutation cannot be detected (nonTR-RTH). Elevated thyroid hormone and non-suppressed TSH in the blood, goitre and variable other clinical symptoms are typical for the disease. Manifestation is often mild and many cases may be even without clinical symptomatology. Cardiac symptoms (mainly dysrhythmias) may be confused with symptoms of hyperthyroidism. Different tissue sensitivity to thyroid hormones causes contemporary presence of symptoms of hypo- and hyperthyroidism. Differential diagnosis of RTH includes more prevalent causes of elevated thyroid hormones with non-suppressed TSH as drugs, non-compliance, biochemical interference and TSH-secreting pituitary adenoma. The treatment of RTH is symptomatic and thyroidectomy should be avoided, if it is possible. Recently, thyroid hormone analogues (e.g. 3,5,3´-trijodothyroacetát) can be used to normalize of thyroid parameters, alleviate of symptoms and achieve goitre regression.