There have been multiple reports regarding the growth hormone (GH) secretion in patients with Prader–Willi syndrome (PWS). However, none have compared GH secretion in children with deletion group to those with maternal uniparental disomy (UPD). We evaluated the GH secretion in pediatric patients with PWS. Seventy-six patients with a deletion (n = 55) or UPD (n = 21) were studied. The secretion of GH by insulin stimulation in the patients with UPD (3.6 ± 2.2 ng/ml) was significantly lower than those with deletions (peak GH level: 11.1 ± 8.6 ng/ml; P = 0.0013). We also compared the response to GH replacement therapy. Yearly improvements in height standard deviation score (SDS) were similar in the two groups (first year SDS: 0.47 ± 0.47, deletion; 0.68 ± 0.26, UPD; P = 0.14). © 2012 Wiley Periodicals, Inc.