Generalized resistance to thyroid hormone (GRTH) is an inherited disease that is usually suspected when elevated serum thyroid hormone levels are associated with nonsuppressed thyrotropin. Often these test results are obtained because of short stature, decreased intelligence, and/or hyperactivity with learning disability noted in childhood and adolescence, or because of goiter in adulthood. We detected GRTH at birth by analysis of blood obtained during routine neonatal screening. The proposita, born to a mother with GRTH, had a thyrotropin level of 26 mU/L and a corresponding thyroxine concentration of 656 nmol/L (normal, 84 to 232 nmol/L). Administration of thyroid hormone in doses eightfold to 10-fold above replacement levels (liothyronine sodium, 21 micrograms/kg per day, and levothyroxine sodium, 44 micrograms/kg per day) were required to reduce serum thyrotropin to normal levels without induction of hypermetabolism. This case, and the retrospective finding of high thyroxine levels in five newborns subsequently diagnosed as having GRTH, suggest that measurement of thyroxine at birth, in conjunction with thyrotropin, could allow the early detection of GRTH.