Aim: To develop methods to identify factors associated with a favorable outcome in GH-treated children with idiopathic short stature (ISS). Methods: From 4,685 children listed as having ISS within KIGS (Pfizer International Growth Database), we studied (a) the prediction model group (n = 657) to develop the first-year prediction model, and (b) the near adult height group (NAH; n = 256) which received GH for >4 years to develop descriptive models for adult height and overall height gain. Results: NAH group at GH start: age was 10.0 years, height –2.5 SD score (SDS), weight –2.3 SDS, height minus mid-parental height (MPH) –1.5 SDS; GH dose 0.19 mg/kg/week. Height gain was 1.1 SDS at a median age of 17.2 years. Growth response correlated positively with GH dose and weight at the start of GH treatment, and negatively with age and height SDS minus MPH SDS. The model explains 39% (error SD 1.2 cm) of the variability. Adult height correlated (R<sup>2</sup> = 0.64) positively with height at GH start, MPH and the first-year responsiveness to GH, and negatively with age. Conclusions: Prepubertal children with ISS who show an appropriate first-year response to GH are likely to benefit from long-term treatment, even on low GH dosages.