Obesity research has recognized that there are many factors contributing to this devastating disorder. Much debate has arisen among scientists to develop models that might be useful in understanding why obesity has become a major health problem and epidemic. However, much of the current debate has been fractious and causes of obesity have been attributed solely to behavior or fast food, personality issues, depression, addiction, or genetics. One of the neurohormonal and genetic causes has been found in Prader-Willi syndrome (PWS), which results in excessive, pathologic reinforcement of food. We have studied PWS to delineate the neurobiology so that environmental cue stimulation may be explained for PWS. Neuroimaging studies have shown that appetizing food and food cues are associated with appetite stimulation. Appetite control is poor in PWS, thus food cues play a major role in its regulation. Hence, PWS may be the genetic model of choice for obesity.