Abstract Objective: To present relevant and updated information on the status of hypothyroidism in the pediatric population (newborn infants to adolescents). Sources: Original and review articles and books containing relevant updated data. Summary of the findings: This review addressed data on the etiopathogeny of hypothyroidism and on the importance of screening for congenital hypothyroidism to assure early diagnosis and treatment of the newborn. We point out the difficulties experienced in the handling of subclinical hypothyroidism; we also address the importance of diagnosing autoimmune Hashimoto’s thyroiditis, the high incidence of the disease among adolescents, mainly females, and the occurrence of a severe neurological condition, Hashimoto’s encephalopathy. We indicate situations in which severe hypothyroidism may lead to puberty disorders (precocious or delayed puberty) and describe the importance of transcription factors in thyroid embryogenesis. Diagnostic and therapeutic criteria are also addressed. Conclusion: Thyroid hormones are necessary for normal growth and development since fetal life. Insufficient production or inadequate activity on the cellular or molecular level lead to hypothyroidism. These hormones are necessary for the development of the brain in the fetus and in the newborn infant. Neonatologists and pediatricians deal with child development issues in their practice, and many of these issues start during intrauterine life. Currently, with neonatal screening, neonatologists and pediatricians can prevent irreversible damage through early treatment. They should also be alert for dysfunctions such as subclinical hypothyroidism and Hashimoto’s thyroiditis, which may provoke damage not only to growth, but also to the neurological and psychological development of these children and adolescents, thyroid hormones, thyropathies, thyroid failure, pediatric hypothyroidism, thyroid deficiency.