The role of the thyroid hormone in the regulation of carbohydrate metabolism is evident from the alterations of the latter which follow changes in thyroid function. Increased rate of absorption of ingested sugars, 1 slight hyperglycemia, 2 and glycosuria 3 often occur in thyrotoxicosis, 2 whereas a decreased rate of absorption of sugar occurs in hypothyroidism. 1 These alterations of carbohydrate metabolism associated with changes in thyroid function are rarely of any clinical significance in the nondiabetic individual. However, changes in thyroid function produce marked alteration in the impaired carbohydrate metabolism of patients with diabetes mellitus; the severity of diabetes is increased in the presence of thyrotoxicosis, 2 and often ameliorated by hypothyroidism. 4 Likewise, diabetes is more frequent in patients with thyrotoxicosis than in the general population, 5 whereas hypothyroidism and diabetes mellitus rarely develop in the same patient.Thirty-three cases of hypothyroidism and diabetes have been reported. The diabetes preceded the hypothyroidism in eighteen of the cases, 2 ' 5~14 and in twelve it developed while the hypothyroidism was being treated. 2 -6 > 7 > 15~21 In only three patients were the two diseases diagnosed at the same time. 2 ' 22> 23 Eight other cases reported as instances of hypothyroidism coexisting with diabetes mellitus are unacceptable because of inadequate evidence for diagnosis of hypothyroidism; in two cases the diagnosis of diabetes was also in question. 24 " 29 Diabetes and hypothyroidism have occurred in patients with various types of multiple glandular disorders: pituitary myxedema, 30 pituitary tumor, 31 and pseudopituitarism. 32 -34 The case report by Schuman 30 is the only example of diabetes mellitus and pituitary myxedema not associated with evidence of other pituitary failure or tumor. The possibility that some of the cases referred to above were instances of pituitary myxedema cannot be evaluated since the response to thyrotropic hormone 35 which would separate primary hypothyroidism from pituitary hypothyroidism was not determined.In view of the rarity of reports of cases of diabetes mellitus associated with hypothyroidism it was considered of interest to present the case studies of two patients who had both diseases. One was a case of spontaneous myxedema with impaired carbohydrate tolerance in which clinical signs of diabetes mellitus developed after nine years of treatment with thyroid substance. The second case was that of an untreated adult cretin.Case i. A. P., a forty-nine-year-old woman clerk, was admitted to the Medical Service of Jefferson Medical College Hospital in 1944. She complained of asthenia, increasing weight, hypersomnolence, and sensitivity to cold for the past six years. The menstrual periods ceased in 1936. She also was diagnosed as having a paranoid-schizophrenia.At physical examination the pulse varied between 50 and 60 and the blood pressure was 100/62. The hair was dry, coarse, and somewhat sparse. The complexion was pale and pasty and th...