On the basis of strong clinical evidence, congenital hypothyroidism should be identified and treated early to avoid potentially profound cognitive deficits. On the basis of strong clinical evidence, the dose of levothyroxine is higher at early ages and progressively decreases into adulthood. On the basis of observational studies and consensus, children with congenital hypothyroidism and a eutopic thyroid gland should discontinue levothyroxine treatment at age 3 years to determine whether their hypothyroidism was transient. On the basis of observational studies, most patients with Hashimoto thyroiditis present with a goiter and without hypothyroidism. On the basis of observational studies, subclinical hypothyroidism is more common among obese children. On the basis of strong clinical evidence, children with central hypothyroidism should have other pituitary hormone deficiencies ruled out.