• Important criteria for judging the status of adolescent patients with respect to the thyroid are the measurement of the uptake of radioactive iodine by the thyroid, the measurement of protein-bound iodine in the plasma, the response of both measurements to administration of the thyroid-stimulating hypophysial hormone, the basal metabolic rate, the serum cholesterol level, and the skeletal age as measured by hand-wrist roentgenograms. In one case here described, inadequate treatment of congenital cretinism had resulted, by the age of 13 years, in physical, emotional, and intellectual retardation; in a second case, myxedema resulted in pseudo-obesity and retarded skeletal growth; in a third, the skeletal age was two years less than the chronological age of 17 years, and sexual maturation had barely begun. Medication with desiccated thyroid had strikingly beneficial effects in these three. A fourth patient appeared to be overweight and had a low basal metabolic rate by surface-area standards; by height standards, however, his basal metabolic rate was found to be normal. Other criteria also showed that his thyroid status was normal. On suitable dietary management alone the changes of adolescence in this patient were completed normally without thyroid.