THE FIRST classic descriptions of inherited goiter were made simultaneously by Osier (1) and Pendred (2) over 80 years ago. Eleven years after their reports, Garrod (3) developed the concept of inborn errors of metabolism. Our understanding of inborn errors of thyroid metabolism awaited the development of sophisticated biochemical investigative tests pioneered by Stanbury just over 30 years ago (4). Since then there has been an enormous growth of our knowledge of these disorders, which has, pari passu, greatly assisted our understanding of normal thyroid physiology. Nine major biochemical defects have been defined consisting of over 20 heterogeneous subgroups. The detailed molecular mechanism in each defect has been only partially elucidated and much remains to be discovered. This paper critically reviews our current knowledge of these defects, their biochemistry, clinical presentation, genetic patterns and methods of investigation. Their relationship to thyroid carcinoma, and the management and treatment of these conditions are also discussed.