The incidence of malignant disease of the thyroid gland is low. Various observers have shown that it does not rise much above 1 per cent for all autopsies. Wilson1 estimated its occurrence at 0.11 per cent, Hinterstoisser2 at 0.27 per cent and Wegelin3 at 1.04 per cent. In spite of considerable study (von Eiselsberg;4 Langhans;5 Kocher;6 Trotter;7 Klose and Hellwig;8 Rogers;9 Meleney;10 Carrel;11 Speese and Brown;12 Bloodgood;13 Balfour;14 Simpson;15 Wilson;1 Ewing;16 Graham17), the diagnosis of malignant disease of the gland, both clinical and histologic, remains difficult. The disease in at least one third of the cases is diagnosed incorrectly prior to operation, and it is probable that the condition frequently is unrecognized even after operative exposure. Hitherto the pathologic study of malignant neoplasms of the thyroid gland has been conducted from the