Resistance to thyroid hormones (RTH) is an inherited syndrome characterised by reduced target tissue responsiveness to these hormones. In the recent years, it has become clear that RTH is probably much more common than is generally recognised, and is often misdiagnosed and inaccurately treated. Subjects suffering from RTH have raised serum thyroid hormone levels and raised or inappropriately normal thyrotropin levels. Two major forms of a clinical presentation of this disorder are asymptomatic or slightly symptomatic subjects with generalised resistance and patients with thyrotoxic features suggesting predominant pituitary resistance. Surprisingly, these various clinical situations are determined by the same genetic defect. In this paper, aetiology, symptoms, clinical classification, diagnosis and treatment of RTH are reviewed with putting special emphasis on the results of recently published studies.