BACKGROUND: Children with Prader-Willi syndrome (PWS) have abnormal body composition and impaired growth. Short-term GH treatment has beneficial effects. OBJECTIVES: The aim of the study was to investigate effects of long-term continuous GH treatment on body composition, growth, bone maturation, and safety parameters. SETTING: We conducted a multicenter prospective trial. DESIGN: Fifty-five children with a mean +/- sd age of 5.9 +/- 3.2 yr were followed during 4 yr of continuous GH treatment (1 mg/m(2) . d). Data were annually obtained in one center: fat percentage (fat%) and lean body mass (LBM) by dual-energy x-ray absorptiometry, height, weight, head circumference, bone age, blood pressure, and fasting IGF-I, IGF binding protein-3, glucose, insulin, glycosylated hemoglobin, total cholesterol, high-density lipoprotein, and low-density lipoprotein. sd scores (SDS) were calculated according to Dutch and PWS reference values (SDS and SDS(PWS)). RESULTS: Fat%SDS was significantly lower after 4 yr of GH treatment (P