Providing the most current information on the function of human growth hormone (GH) and the consequences of its deficiency, this practical yet comprehensive text is divided into three sections. Part one describes the mechanisms of GH secretion and action, including the physiology of GH and its regulation by sex steroids and thyroid hormones, the effects of both under nutrition and obesity on GH secretion, and the metabolic effects of human recombinant GH therapy. The second section covers diagnostic strategies and tests for GH deficiency in both children and adults, including MRI of the pituitary. The final section describes the different etiologies of GH deficiency, from molecular mechanisms and gene abnormalities to cranial radiation and traumatic brain injury, along with syndromes related to this deficiency.