Two cases of thyroglossal duct cyst carcinoma are presented and the world literature is reviewed. There are only 74 cases reported to date. In nearly all the cases the clinical diagnosis was thyroglossal cyst. Although the great majority of the tumours were papillary adenocarcinomas, 13-15 per cent were of other histological types. The treatment has been quite variable, but the most common initial treatment was Sistrunk's (1928) operation. Following the establishment of the diagnosis of malignancy, thyroidectomy was done in several cases, but it failed to show any evidence of malignancy in most of the thyroids removed, which establishes firmly the de novo origin of these tumours from the thyroglossal duct remnant. In only one case had tumour disseminated to distant organs, the lung, liver, etc. The scepticism as to whether some of the carcinomas associated with thyroglossal duct remnants may not in fact represent metastases from a small primary tumour of thyroid gland is examined. It appears that, though a possibility of primary or metastatic tumour in the thyroid does exist, the probability does not appear to be high. From our own experience it is suggested that local excision followed by radiotherapy, irrespective of recurrence, may be worth considering for the treatment of such carcinomas.