The Tthyroglobulin (Tg) protein is the essential fundament toto thyroid hormone synthesis, a key player playing a vital role in the regulation of metabolism, development and growth and serving as intraglandular iodine storage. Its structure is conserved among vertebrates. Tg is delivered through the secretory pathway of the thyroid follicular unit to the central colloid depository, where it is iodinated at specific tyrosine sites to form mono- or diiodotyrosine, which combine to produce triiodothyronine (T3) and thyroxine (T4), respectively. Synthesis of these hormones depends on the precise 3D structure, iodination capacity and post-translational modification of Tg. The Tg structure is overall conserved among vertebrates and , which and structural information has long been remained unknown missing despite decades of research until recently structural information has been made available on human thyroglobulin (hTg) originating from recombinant hTg and endogenous hTg from patients with goitres. Here, we present the cryo-electron microscopy structure of native and fully functional human thyroglobulin (hTg) originating from healthy human thyroid glands, to a global resolution of 3.2 Å. We used LC-MS experiments to The structure provides detailed information on the location of the hTg hormonogenic sites by revealing native iodination, and reveals the position as well as the role of many of its glycosylation sites and other post-translational modifications. Our results offer structural insights into thyroid hormonogenesis of natively functional hTg and provide a fundamental understanding of clinically relevant hTg mutations, which can improve treatment of thyroid diseases.