The relationship, or rather the lack of relationship, between diseases of the thyroid and pregnancy is not well understood, and most of the literature on the subject is confusing and often misleading. This may be attributed, first, to a failure to differentiate clearly the various thyroid diseases, and, secondly, to carelessness in differentiating and excluding those syndromes which simulate thyroid disturbances, but are not due to them. The various types of goiter, according to the classification of H. S. Plummer,1are: (1) diffuse colloid goiter of adolescence; (2) adenomatous goiter without hyperthyroidism; (3) adenomatous goiter with hyperthyroidism, and (4) exophthalmic goiter. Marine and Kimball2have shown that diffuse colloid goiter and probably also adenomatous goiter without hyperthyroidism can be prevented in school children by administration of iodine. The development of these diseases is associated, as H. S. Plummer has pointed out, with potential, if not actual, hypothyroidism. The