This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Prader-Willi syndrome (PWS) is a rare genetic disorder associated with obesity. Early in life, children with PWS demonstrate poor weight gain and low muscle tone. This study evaluates the effect of growth hormone (GH) upon these conditions. This randomized controlled study will compare children with PWS treated with GH compared to control PWS children. Outcomes will include measuring body fat, muscle mass, energy expenditure, hormonal levels an