 Methodology: This study is a double blind control study. We will include 24 PWS patients, aged over 18 years recruited at the Hendaye Marine Hospital associated with the PWS reference center whose coordination is in Toulouse. The hospital routinely receives PWS adults for a 4 weeks stay which gives optimal conditions for the establishment of this study. Patients are separated into 2 groups matched one by one on the sex and IQ. One group receives the OT, the other a placebo. Forty five minutes after inhalation, all of the patients are evaluated on their social comprehension thanks to psychometric tests. Furthermore, an analysis based on observation sheets allows us to score daily stress, anxiety and eating behavior. These sheets serve for the comparison between 2 days before and 2 days after the nasal spray on the above described scoring components. 