Prader-Willi syndrome is a genetic disorder caused by the loss of function of specific genes on chromosome 15, characterised by weak muscle tone and feeding difficulties in infancy followed by an insatiable appetite and severe obesity from early childhood. The hypothalamus, the brain’s appetite control centre, fails to register satiety, so affected individuals experience constant, overwhelming hunger (hyperphagia) and will eat compulsively without intervention. Management centres on strict food environment control, locked kitchens, supervised meals, growth hormone therapy to improve body composition, and lifelong supervision, since the drive to eat never abates. Intellectual disability and behavioural challenges commonly accompany the condition. Prader-Willi is the starkest illustration of appetite’s neurological basis: hunger is a brain signal, and when the wiring fails, willpower is irrelevant.