Subclinical hyperthyroidism is a clinical condition with a laboratory diagnosis defined as a suppressed below the normal range TSH level and normal free thyroxine and triiodothyronine levels. The condition is frequently recognized but its long-term clinical consequences are constantly debated. There is little good evidence available to guide the management of patients with subclinical hyperthyroidism. This review summarizes current state of knowledge on the prevalence, aetiology, clinical consequences and treatment of subclinical hypertyroidism.