The myriad of identified genes involved in the regulation of the differentiation and functional integrity of the anterior pituitary lobe, neurohypophysis, thyroid and adrenal glands, ovaries, testes, and pancreatic beta cells are listed and the variations in the composition of those genes that alter gland or cell formation, growth, maturation and activity are discussed. Genetic control of the synthesis, secretion, and action of the six major hormonal products of the adenohypophysis (growth hormone, thyrotropin, prolactin, adrenocorticotropin, luteinizing hormone, follicle stimulating hormone) are detailed. Gene variants that result in either decreased or increased secretion of the anterior pituitary lobe hormones and/or tumorigenesis are described. The role of insulin-like growth factor-I in the signaling pathway of growth hormone modulated effects and the consequences of genetic errors in this circuit are discussed. Detailed discussions of the gene mutations resulting in impaired development of the anterior pituitary lobe, decreased or excessive synthesis of its products, and abnormalities of the peripheral activity of these hormones are presented. The clinical and biochemical abnormalities due to genetic variants that lead to impaired formation or function of the posterior pituitary lobe (e.g., diabetes insipidus), thyroid gland (e.g., congenital hypothyroidism), adrenal cortex (e.g., congenital adrenal hyperplasia, familial isolated glucocorticoid deficiency, adrenoleukodystrophy), adrenal medulla (e.g., pheochromocytoma), ovary, testis, and pancreatic beta cells (e.g., congenital hyperinsulinemic hypoglycemia, neonatal diabetes mellitus, maturity onset diabetes of the young) are also recorded. Discussed too are the gene mutations associated with the autoimmune polyendocrinopathies and multiple endocrine neoplastic syndromes. Clinical disorders (e.g., Noonan, Costello, cardio-facial-cutaneous syndromes) that result from genetically mediated malfunction of the intracellular mitogen activated protein kinase signal transduction pathway are explored. Monogenic forms of obesity are also presented.