Hyperthyroidism is a pathological ailment wherein excess thyroid hormone is synthesised and secreted by the thyroid gland. It is characterised by ordinary or excessive thyroid radioactive iodine uptake (thyrotoxicosis with hyperthyroidism or genuine hyperthyroidism). Thyrotoxicosis without hyperthyroidism is resulting from extrathyroidal assets of thyroid hormone or by a release of preformed thyroid hormones into the move with a low thyroid radioactive iodine uptake (table 1).1 Hyperthyroidism can be overt or subclinical. Overt hyperthyroidism is characterized by way of low serum thyroid-stimulating hormone (TSH) concentrations and raised serum concentrations of thyroid hormones: thyroxine (T4), tri-iodothyronine (T3), or both. Subclinical hyperthyroidism is characterised by means of low serum TSH, but everyday serum T4 and T3 concentrations. We do now not discuss subclinical hyperthyroidism right here, however it become currently reviewed in every other Lancet Seminar.2