Prader-Willi syndrome (PWS) is a rare entity that is, however, the most frequent cause of genetic obesity, with an alteration located on chromosome 15q11-13. The diagnosis is based on a set of criteria, in particular, generalized hypotonia and feeding difficulties during the neonatal period, accompanied by cryptorchidism secondary to hypogonadism. Over the long term, the patients present a higher risk of metabolic complications, among others, that affect the quality of life. Early diagnosis is essential for the purpose of initiating early multidisciplinary treatment involving endocrinologists, physical therapists and psychologists.

We conclude that PWS should be included in the differential diagnosis in any case of neonatal hypotonia, and that, as in our case, early diagnosis permits the patient to benefit from a multidisciplinary intervention from the very start, a circumstance that reduces the incidence of complications and improves qua¬lity of life.