Observations regarding caloric intake, growth, and food-related behavior of 14 children with Prader-Willi syndrome have shown that they need fewer calories than normal children to maintain their weight in an appropriate weight channel, and that they exhibit peculiar food-related behavior that in some instances is present before the onset of obesity. Most of them can be prevented from gaining excessive weight or can lose weight if they and their caretakers receive appropriate counseling on how to provide low-calorie food and how to make other food inaccessible. In 12 of the 14 children, a reasonably successful weight-control program was achieved for up to five years. A biological basis for many of the noted observations is assumed, but the exact nature of the defect remains elusive.