Several recent advances in our knowledge of thyroid physiology have broad application to the diagnosis and management of thyroid disorders. Foy in the thyroid, more than other end-ocrine organs, pathophysiology can he translated directly into the diagnosis and management of thyroid disease. Graves' disease is a syndrome including goiter with hyperthyroidism, exophthalmos and dermopathy. The pathogenesis of Graves' disease is not yet clearly identified, but various autoantibodies ta the thyroid gland and immunapathalogic studie indicate that autoimmune processes are involved in the pathogenesis of the disease. The diagnosis and management of Graves' disease are largely dependent on radionuclide technique as radioimmunoassay, radioactive iodine therapy and so on. Several laboratory tests are also developed to determine the remission of this disease including TRH stimulation test, T3, suppression test and detection of thyroid stimulating immunoglobulins. Autoimmune thyroiditis is almost certainly a primary immunologic disease and the incidence tends to increase recently, mainly due to the application of biopsy technique is thyroid diseases. Thyroid nodules have been a great challege to physicians because of the possibility of malignancy. But recently, cytologic examination of thyroid aspirate provides a very simple and also reliable diagnostic method in patients with thyroid nodules. In 163 patients with thyroid nodules, only 19.3% was revealed to be malignant. Therefore cytglogic examination of thyroid aspirate and thyroid biopsy should be included in the diagnosis of nodular patients prior to surgical intervention. In this paper, a comprehensive review is presented on the pathogenesis, clinical features, laboratory findings and therapeutic modalities of various thyroid diseases on the basis of over 80 researches performed during the past 20 years at radioisotope clinic, Seoul National University Hospital.