Background: Abnormal body composition, with low muscle mass and increased fat mass, as well as short adult stature are common features in Prader-Willi syndrome (PWS), as in growth hormone (GH) deficiency. Methods: We followed a cohort of 22 genetically verified patients with PWS from the start of GH (Genotropin®) treatment at the median age of 6.9 years (4.9–11.3) to near-adult height at 18.1 years (16.4–21.2). The patients were treated with a median GH dose of 0.03 mg/kg/day (0.02–0.03) for a median duration of 10.2 years (6.9–11.5). Results: All patients reached near-adult height within midparental height median –0.5 SDS (–1.4 to 0.7) and 0.9 SDS (0.1–1.9) for girls and boys, respectively. The body composition improved but did not normalize. Only 7 of the 22 patients were reported to be in puberty. None of the patients were reported to be on sex hormone substitution which might contribute to not reaching a normal body composition. No serious side effects were reported when the caloric intake was controlled to maintain an appropriate body weight. Conclusion: GH treatment in children with Prader-Wili syndrome normalizes adult height and improves body composition.