A total of 54 previously untreated patients (15 girls, 39 boys) with poor growth due to idiopathic growth hormone deficiency (IGHD) were treated with human growth hormone (hGH), continuously up to 4 years. All of the patients had a peak hGH level which was below 10 ng/mL after at least two pharmacological tests and/or blunted physiologic hGH secretion, and their height was below -2.5 s.d. for age and gender. After the 1st year of therapy, height velocity (HV) increased significantly when compared with baseline (from 3.18 +/- 0.76 cm/year to 9.17 +/- 1.03 cm/year; P < 0.001), declined during the 2nd year and then remained significantly higher than pretreatment HV. When considering improvement in height expressed by height standard deviation score (SDS), during the therapy all of the patients showed a significant gain +/- 1.72 +/- 1.09 (from -4.11 +/- 0.61 to -2.21 +/- 0.48). The height values were significantly higher than pretreatment, but remained below -2 s.d. after 4 years of hGH therapy in our patients. Increased height velocity has been sustained, but height improvement after therapy was inversely correlated to height SDS for chronological age of patients at the start of therapy. In conclusion post-treatment height has been shown to be related to height deficit at the beginning of therapy. Therapy was well tolerated with no local or systemic adverse effects or acceleration of bone age.