The thyroid gland is an organ with internal secretion. Like other endocrine organs, the thyroid is extremely well blood-circulated. It is located at the front of the neck, consisting of two lobes connected by a thin section, an Isthmus. Its follicles produce two major hormones, thyroxine (T4) and triiodothyronine (T3). After binding to nucleus receptors, these hormones act on cells of almost all tissues, altering the expression of a number of gene products. They are necessary for the normal development of the brain and somatic tissues of the fetus and newborn, and they monitor the metabolism of proteins, carbohydrates and fats at every age. In order to maintain normal metabolic activity in the body, a specific amount of thyroid hormone must be secreted which is enabled by special mechanisms that act through the hypothalamus and adenohipophysis. If the thyroid gland secretes too much or not enugh hormones the disease occurs, such as hyperthyroidism and hypothyroidism. Thyroid diseases are among the most common of all endocrine disorders. They are diagnosed by various methods: physical examination, laboratory processing, imaging and radiological examination. Serum thyrotropin (TSH) is the most specific and the most sensitive indicator of biological effects of thyroid hormones. In hypothyroidism and hyperthyroidism, treatment is carried out with drugs. In drug-unregulated hyperthyroidism, meaningly enlargement of the thyroid gland, diagnostically unclear thyroid nodules, and in thyroid cancer, treatment is primarily surgical. It is important to note that thyroid cancer is the most common malignant tumor of the endocrine system. Today, thyroid surgeries are a safe method of treatment with relatively rare complications. In addition to surgical treatment, radioactive iodine therapy is also used.