We report four children who presented no evidence of primary hypothyroidism in the neonatal period, either clinically (normal growth velocity) or biochemically (normal plasma levels of thyroid stimulating hormone and/or thyroid hormone). However, in early childhood, these children developed severe hypothyroidism due to dyshormonogenesis. We conclude that apparently normal thyroid function in the neonatal period does not preclude the development of severe hypothyroidism due to thyroid dyshormonogenesis later in childhood.