Cervical teratomas are uncommon neoplasms, although the commonest neck tumors in newborns and infants. Presence of associated thyroid tissue often causes speculation as to the site of origin, ie, arising from within thyroid, adjacent soft tissue with secondary involvement of thyroid, or as innate part of a cervical teratoma. Twenty-eight cases of cervical teratomas were identified over 75 years, including 11 cases containing associated thyroid tissue. Clinical history, treatment, and follow-up were reviewed and the neoplasms analyzed regarding location, size, degree of maturity, and relative arrangement of thyroid and other tissues. All thyroid teratomas were congenital, measured 3.5 to 13.5 cm in diameter (median size, 6.9 cm), and were resected. Follow-up ranged from 1 to 45 years (median, 17 years) without recurrent disease in any patient. Neuroglial tissue predominated in 10 of 11 tumors. Intimate admixture of thyroid and other tissues with or without surrounding fibrous pseudocapsule was present in 8 cases, suggesting thyroid as origin. Histologic immaturity in congenital thyroid teratomas is not the harbinger of adverse behavior as seen in adolescents and adults. Intimate intermingling of thyroid tissue with teratoma and presence of a pseudocapsule seem to be the most significant criteria for establishing thyroid as origin.