Thyroglobulin (TG) is a dimeric glycoprotein specific to the thyroid gland which belongs to the type-B carboxylesterase/lipase family. It is the precursor of the iodinated thyroid hormones triiodothyronine (T3) and thyroxine (T4). Variations in TG are associated with susceptibility to autoimmune thyroid disease type 3. Defective or impaired TG synthesis usually results in congenital goitrous hypothyroidism, virtual absence of TG in thyroid tissue, and the presence of an elevated concentration of iodoalbumin. The final result of these abnormalities is a decreased rate of T3 and T4 synthesis. Thyroglobulin is found in normal thyroid and differentiated thyroid carcinoma cells, but not undifferentiated thyroid. Thyroglobulin is a useful marker for identification of tumors with thyroid origin.