We assessed bone mineral density (BMD) and body composition in children with Noonan's syndrome (NS) before and during growth hormone (GH) treatment. Sixteen children (12 boys, 4 girls) with NS aged 5.8-14.2 (mean 10.0) years were studied for 2 years. Anthropometry, BMD measurements by radiographic absorptiometry and bioimpedance measurements (Akern-BIA 101/S) were performed at baseline and after 3, 6, 12 and 24 months. Daily GH dosage was 0.05 mg/kg. Trabecular volumetric BMD was normal; cortical BMD was in the lower normal range at baseline and slightly increased over the 2 years. Fat free mass and total body water were below normal at the start and increased significantly over the first 3 months, with a slight increment thereafter. Percentage fat mass decreased over the first 6 months and increased thereafter. These findings are comparable to the data on body composition in short normal children and girls with Turner's syndrome treated with GH.