['Prader-Willi syndrome is a neurogenetic disorder, with characteristics such as obesity, short stature, muscular weakness, intellectual deficiencies and deviant social behaviour. This study evaluated whether growth hormone treatment of children with Prader-Willi syndrome resulted in possible and lasting effects on their cognition and behaviour.', 'We randomised six girls and 13 boys to either a treatment group or a control group. The treatment group received growth hormone (Genotropin(®) 0.033 mg/kg/day) for 2 years, while the control group did not receive treatment in the first year and then received a double dose in the second year. Treatment was then stopped in both groups for 6 months.', 'Both groups showed the same intellectual disabilities at the start of the study, and no difference was found after the first and second years. The parents reported that the children showed increased vitality during treatment. When treatment was stopped, the children showed a marked exacerbation of behavioural problems, a significant increase in body fat and a decrease in insulin-like growth factor 1 levels.'] Does growth hormone treatment improve vitality and behavioural issues in children with Prader-Willi syndrome?