PWS is characterized by central hypotonia and feeding difficulties during infancy followed by excessive eating, rapid weight gain, and central obesity in early childhood. Children with PWS exhibit characteristic facial features including bitemporal narrowing, almond-shaped palpebral fissures, and a down-turned mouth. Additional diagnostic characteristics of PWS include global developmental delay, mild to moderate intellectual disability, distinctive behaviors, short stature, hypopigmentation relative to other family members, small hands and feet, and hypogonadism manifesting as genital hypoplasia, incomplete/delayed puberty and, in the majority of cases, infertility. The neurobehavioral phenotype in individuals with PWS includes hyperphagia, temper tantrums, aggression, specific repetitive and ritualistic behavior, stealing and lying, skin picking, mood and sleep disturbances. Consensus diagnostic criteria were first established in 1993 and revised in 2001 to aid in the recognition of the disorder.