FAILURES in the treatment of persistent thyroglossal ducts and cysts may be due to either of two factors: lack of understanding of the development of the thyroid gland and the persistent ducts and cysts, and lack of definite knowledge of the technique of the surgical treatment. Too often the cysts are merely incised or incompletely excised. The Sistrunk operation, in our opinion the procedure of choice, is inadequately discussed in most texts.We shall first briefly review the development of the persistent duct and cyst and then discuss the Sistrunk operation.DEVELOPMENT OF THE THYROID GLANDThe thyroid appears in human embryos of about 5 mm. in length toward the end of the fourth week. It arises as a diverticulum of the floor of the primitive pharynx and is, therefore, an endodermal derivative. A lateral view of the head of a human embryo at this stage is illustrated in Figure