Tumors of lateral aberrant thyroid tissue offer a particularly fruitful field for the investigator interested in the origins of cancer. In some of the earliest reports of this condition, Hinterstoisser1 pointed out that the tendency to malignant degeneration in these primarily benign tumors is great. When one considers the fact that the dividing line between innocent and malignant tumors is nowhere less sharply drawn than in tumors of thyroid tissue showing the papillary design, it will be seen that intriguing opportunities are offered in the study of this group of neoplasms. Most investigators agree as to the possibility of malignant change, but there is considerable difference of opinion as to the point at which malignancy begins, the criteria of malignancy and the degree of malignancy, once the diagnosis is established. Dunhill2 wrote: "It would seem that these misplaced bits of tissue, whether in the lateral triangle of the