Background/Aims: To investigate whether short-term changes in body composition as a result of growth hormone therapy could be used to predict its growth effect after 1 year in children with growth hormone deficiency (GHD) and children born small for gestational age (SGA). Methods: 88 GHD children and 99 SGA children who started treatment with recombinant human growth hormone were included. Total body water (TBW) and height were measured. After 1 year, patients were divided into adequate and inadequate responders. Results: In GHD and SGA children a sensitivity of 87 and 53%, respectively, and a specificity of 58 and 83%, respectively, were found. The positive predictive values for GHD and SGA children were 73 and 90%, respectively. The negative predictive values were 75 and 32%, respectively. Conclusion: Changes in body composition data measured by TBW are a valuable tool to correctly predict 75% of the GHD children and are only useful in SGA children when the change in TBW is above the cut-off value of 0.7 l/m².