We studied the influence of recombinant human growth hormone (rhGH) on pubertal timing and pubertal growth in children with idiopathic short stature (ISS), and evaluated whether this was different between children with and without intra-uterine growth retardation (IUGR). Twenty-six (18 M, 6 IUGR; 'treated') subjects were treated with rhGH (6-7 days/week, dosage: 14-28 IU/m2 per week [i.e. 0.2-0.3 mg/kg per week]). Fifty-eight subjects (31 M, 9 IUGR; 'controls') were not treated. All subjects attained final height. Prepubertal height gain was significantly larger in the treated children compared to control children (M: 0.66 SDS, 95% confidence interval [CI] 0.41 to 0.92; F. 0.92 SDS, CI 0.58 to 1.26). Pubertal height gain, peak height velocity and duration of puberty were similar for the treated and control subjects. rhGH advanced the age at peak height velocity by 0.7 years (CI 0.3 to 1.0) in boys, and the age at onset of puberty by 1.1 years (CI 0.3 to 1.9) in girls. The gain in final height was 2-3 cm. Age and height SDS at start were the most important predictors for pubertal height gain, total height gain and final height in a multivariate regression analysis. Total height gain of treated subjects with IUGR was less than that of treated subjects without IUGR. In conclusion, rhGH did not affect pubertal growth in children with ISS, and slightly improved their final height. rhGH treatment should be started early to improve height as much as possible before the onset of puberty.