Prader-Willi Syndrome (PWS) is the most common cause of genetic obesity. Hyperphagia and obesity are the most associated concepts with this condition. However, undernutrition secondary to severe hypotonia and feeding difficulties is the predominant initial feature.Objective: to reproduce and communicate the nutritional phases on a series of Chilean cases with PWS.Patients and Method: Cross-sectional study in which clinical records of PWS individuals under nutritional control at the Clínica Santa María in Santiago, Chile between 2017 and 2018 were analyzed. The anthropometric references of the World Health Organization were used to carry out the nutritional assessment. The classification into nutritional phases was according to the Miller criteria.Results: 24 patients from infants to adults were included. All children aged under 9 months were in phase I and had malnutrition or were eutrophic; those between 9 and 25 months were classified in phase 2a; patients between 2.1 and 4.5 years were distributed between phases 1 and 2 and 66% were eutrophic; those between 4.5 to 8 years, 80% were in phase 2a and 2b and obesity begins to appear, and patients over 8 years of age, 75% were in phase 3 and all are overweight or obese. There was an association between nutritional phase and age but not between it and nutritional status.Conclusions: In our series, the nutritional phases described according to age were reproduced according to those internationally described. There was no association between nutritional status and age.El Síndrome de Prader-Willi (SPW) es la causa más frecuente de obesidad de origen genético, siendo obesidad e hiperfagia los conceptos más asociados a esta enfermedad. Sin embargo, la desnutrición secundaria a una hipotonía marcada y dificultad alimentaria, es la característica inicial predominante.Objetivo: Reproducir y comunicar las fases nutricionales en una serie de casos chilenos de SPW.Pacientes y Método: Estudio transversal en que se analizaron registros clínicos de individuos con SPW bajo control nutricional en Clínica Santa María, Chile durante 2017 y 2018. Se utilizaron los referentes de la Organización Mundial de la Salud para la evaluación nutricional. La clasificación en fases nutricionales se basó en los criterios de Miller.Resultados: Fueron incluidos 24 individuos desde lactantes hasta adultos. Todos los menores de 9 meses estaban en fase 1 y eutróficos o desnutridos, entre los 9 y 25 meses aparecen niños en fase 2a. Entre los 2,1 y los 4,5 años se dispersan entre las fases 1 o 2 y 66% estaba eutróficos. Entre los 4,5 a 8 años, 80% está en la fase 2a y 2b y empieza a aparecer la obesidad, sobre los 8 años un 75% está en fase 3 y todos tienen malnutrición por exceso. Se demostró una asociación entre fase nutricional, pero no entre estado nutricional y grupo etario.Conclusiones: En nuestra serie de SPW se reprodujeron las fases nutricionales acorde a la edad descritas internacionalmente. No se demostró una asociación entre el estado nutricional y la edad.