Clinical spectrum and endocrine details of thirteen Turkish children (age 0.3-14.2 years; eight females and five males; ten prepubertal, three pubertal) with growth hormone insensitivity are presented. All patients display phenotypical features of severe growth hormone deficiency. The diagnosis based on height standard deviation score (SDS), basal growth hormone (GH), basal insulin-like growth factor I (IGF-I, IGF-I response in an IGF generation test and growth hormone binding protein (GHBP) measurements. The median height SDS was -7.4 (range -3.2 to -10), weight for height index was 100 (range 81-152) and bone age/height age ratio was 2 (range 1.6-3.3). Endocrine investigations showed a median basal GH concentration of 61.4 mU/l (range 23.5-120 mU/l). Basal IGF-I level was below 10 ng/ml in all patients except one. None of the patients showed a significant IGF-I response to injections of GH (0.1 U/kg body weight for 4 days). The median IGFBP-3 level was 0.23 mg/l (range 0.1-0.56 mg/l). The GHBP level was undetectable in all of 10 patients. The high number of patients in our center may be due to the high rate of consanguinity among the Turkish population and the referral facility of our center in the area. These patients may benefit from the new therapy with recombinant human IGF-I.