Over the past years, great advances have been made in the research of Prader-Willi Syndrome and its treatment options. The results raise hopes that the once depressing outlook for children with PWS and their parents will gradually give way to a much improved quality of life. Clinical research has shown that there is a hypothalamic growth hormone deficiency in PWS and that growth hormone treatment improves body composition, body proportions and physical performance of patients. Increased lean body mass enhances energy expenditure and - provided the energy input can be restrained - children no longer become obese. The disappearance of the obese phenotype in children with PWS who are treated with growth hormone starting before puberty prevents stigmatisation of children and their families in society. The mental retardation and the compulsive behavior disorder will however remain major handicaps which seemingly cannot be influenced by growth hormone therapy. This book provides an overview of the clinical research results as to hormones and metabolism of PWS with special emphasis on growth hormone and growth hormone treatment. Besides the outstanding scientific texts, this volume offers comprehensive photographic material to document the development of selected patients over several years and to illustrate extreme individual changes in the physical appearance and facial expression.