Prader-Willi syndrome (PWS) is a rare disease first described in 1956. It is an important part of mental retardation related to a genetic cause and is one of the leading causes of syndromic obesity in children. It is responsible for physical, psychological and social disabilities of a particular gravity. The diagnosis is evoked on clinical elements and confirmed only by genetic analysis. The management of this disease is multidisciplinary and can be extremely difficult in the teenage age due to behavioral disorders and the total lack of autonomy of patients. We report the case of two patients followed in our training for the treatment of PraderWilli syndrome in adolescence with severe behavioral disorders.