 The role of oxytocin OT is already known in the regulation of satiety but some clinical studies demonstrated that OT participates also in the regulation of social behavior by its implication on a better comprehension of emotion which plays a role on theory of mind and empathy. By the way, these 2 behaviors are deviants for patients with Prader-Willi Syndrome PWS. Actually, no study was led on the effect of OT on PWS patients but Swaab and al in 1995 showed a significant reduction in number and in volume of neurons expressing OT in the paraventricular nucleus of PWS patients. Recent data were obtained studying OT in patients with autism which showed a link between the deregulation of OT and the autistic pathology. Clinical and imaging studies obtained with PWS and autistic populations make us believe that some mechanisms are common between these two pathologies. 