Context: Alterations in the GH-IGF-I axis in short small-for-gestational- age (SGA) children might be associated with abnormalities in bone mineral density (BMD) and body composition. In addition, birth weight has been inversely associated with diabetes and cardiovascular disease in adult life. Data on detailed body composition in short SGA children and long-term effects of GH treatment are very scarce. Objective: To investigate effects of long-term GH treatment on body composition and BMD by dual energy X-ray absorptiometry (DXA) in short SGA children. Design: Longitudinal 6-year GH study with a randomized controlled part for 3 years. Results: At baseline, fat percentage standard deviation score (SDS) and lumbar spine BMD SDS corrected for height (BMADLSSDS) were significantly lower than zero. Lean body mass (LBM) SDS adjusted for age was also reduced, but LBM adjusted for height (LBM SDSheight) was not decreased. GH treatment induced a decrease in fat percentage SDS and an increase in BMADLSSDS. LBM SDSheightremained similar in GH-treated children, but deteriorated in untreated controls. When these untreated controls subsequently started GH treatment, their LBM SDSheightrapidly normalized to values comparable with zero. Conclusion: During long-term GH treatment in short SGA children, fat percentage SDS decreased and BMADLSSDS increased. These effects of GH treatment were most prominent in children who started treatment at a younger age and in those with greater height gain during GH treatment. LBM SDSheightremained around 0 SDS in GH-treated children, but declined to low normal values in untreated controls.