Publisher Summary This chapter reviews the presentations and most common causes of these neuroendocrine growth disorders, highlighting various gene mutations, endocrine syndromes, and acquired defects that result in states of growth hormone deficiency or excess. Growth hormone (GH) is secreted by the somatotrope cells of the anterior pituitary gland. Although its main function is to promote postnatal longitudinal growth, GH exerts numerous additional functions, such as regulation of glucose and lipid metabolism, bone apposition, skeletal and cardiac muscle mass growth, and arterial pressure. Insulin-like growth factor–1 (IGF–1) plays a paramount role in controlling growth and orchestrating its progression. The GH-releasing (GHR) hormone a membrane-bound 626–amino acid glycoprotein which includes an extracellular domain, a transmembrane domain, and an intracellular domain that couples with the JAK-Stat, PI3kinase and MAP kinase pathways. Gigantism refers to a condition characterized by excessive longitudinal growth beyond the patient's genetic target. By definition, this originates during childhood while epiphyseal growth plates are still open.