Subclinical hyperthyroidism is a term used to define a clinical condition in which a reduced serum thyroid stimulating hormone (TSH) level is accompanied by thyroxine and tri-iodothyronine levels within the reference ranges. It is a common condition with the prevalence in the general population estimated on 0.6-16%. Subclinical hypethyroidism may progress to overt hyperthyroidism and is associated with the risk of the development of cardiovascular complications (especially atrial fibrillation), osteoporosis and dementia. Indications for the management of subclinical hyperthyroidism still remain controversial. The aim of this paper is to familiarise the reader with the present state of knowledge on the prevalence, etiopathogenesis, clinical manifestation, diagnosis, potential complications, prognosis and treatment of subclinical hyperthyroidism.