We report a baby born from a mother with strongly positive thyroid stimulation blocking antibody (TSBAB) and nearly undetectable T4 level. This case is a unique model of nearly complete absence of thyroid hormones during fetal and early neonatal life in humans. The infant girl was born by cesarean section, because of fetal bradycardia, after 41 weeks gestation and received mechanical ventilation for 3 days. The TSH level was more than 120 microU/mL in the neonatal thyroid screening. At age 17 days, the results of a thyroid function study showed undetectable free T3 and free T4 concentrations, TSH 550 microU/mL, and TSH receptor antibody (TRAB) 87%. Thyroxine at a dose of 30 microg/day was started at age 17 days. The patient required thyroxine treatment until age 8 months. The brain magnetic resonance image at age 2 months revealed reduced brain size. Her auditory brain stem response was absent at age 2 months. The audiogram at age 4 yr revealed sensorineural deafness of 70 dB. When she was 6 yr of age, motor development remained the same as that at age 4 months. Her height was 106 cm (- 1.5 SD). The results of thyroid function study of the mother 23 days after delivery showed undetectable free T3 and free T4, TRAB 84%, and TSBAB 83%. In conclusion, the outcome of severe thyroid hormone deficiency in utero and early in human neonatal life was normal physical growth, fetal distress resulting in cesarean section, difficulty in the onset of breathing, permanent deficit in auditory function, brain atrophy, and severely impaired neuromotor development despite the start of an adequate dose of thyroxine replacement during the neonatal period.