Subclinical hyperthyroidism is defined as normal thyroid hormone level in serum but low serum thyrotropin TSH concentration in an asymptomatic individuals. The article described prevalence, pathogenesis, causes, clinical symptoms and diagnostic criteria of subclinical hyperthyroidism and is especially focused on patients with this thyroid dysfunction induced increase risk for development of atrial fibrillation and a decrease in bone mass in the case of postmenopausal women. It is not clear whether and when this pathology should be treated but the problem is important because of 4% patients per year which can possible develop overt hyperthyroidism. Most of the authors conclude that a treatment is required in selected cases or under special circumstances only.