Currently, technical methods to obtain precocious and reliable diagnosis of thyroid disorders are available for physicians. Therefore today, patients affected by mild hypo- or hyperthyroidism are more often diagnosed when they are still asymptomatic; these mild forms of thyroid disorder are known as subclinical hypo- and hyperthyroidism. In comparison with '80ties, over the last few years we have observed that patients come to endocrinological examination for subclinical forms of thyroid disorders (particularly for hypothyroidism) more frequently than for severe thyroid diseases. However, before to start a therapy, it is necessary for these patients to determine the causes of subclinical hypo- and hyperthyroidism. The main goals of therapy are to reduce the prevalence of cardiac arrhythmia and osteoporosis of patients with subclinical hyperthyroidism, and to slow down the course of arteriosclerotic disease (linked to hyperlipidemia and/or to hyperhomocysteinemia) of patients with subclinical hypothyroidism.