 Recent clinical studies showed that the oxytocin OT, next to its long-time known actions lactation, satiety, participates in the regulation of the social behavior. 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 suggest a link between OT and the autistic pathology: the existence of a lower plasmatic rate on OT and the association with a polymorphism of the OTs receptor for autistics patients. Because OT has a role on the pro-social behavior and on the nervous control of the stress, the hypothesis on which a deficit in OT would play a role in the abnormalities of the social behavior was advanced. Moreover, certain features of the autistic spectrum disorder can be found in PWS patients. Moreover, a recent study has shown that OT administered by intra-nasal spray reduces psychosocial stress and increases the confidence in each other in healthy volunteers. The PWS is a genetic pathology and some clinical features are very similar to the autistic pathology. The PWS is the most common cause of syndromic autism. Data from the literature and a collaborative study conducted between our team and the Prof. B. Rogés team suggests that these two pathologies share common pathophysiological mechanisms. To our knowledge, no study with the OT was conducted in people with PWS. We want to conduct a pilot study in adult patients with PWS. Given the severity of this disease, related to socialization disorders, significant anxiety and overeating, and with no effective therapy, this justifies the pilot study. Moreover, side effects of OT are almost nonexistent when used by intra-nasal. 