Children with simple obesity (SO) show increased linear growth with normal or high serum insulin-like growth factor-I (IGF-I) levels during prepubertal period, despite low GH secretion. We measured IGF-I, IGFBP-1, GHBP and other factors to clarify the hormonal relation between the nutrition and the linear growth in SO and compared these factors with children with normal short stature (NS). Subjects were 23 SO and 19 NS children, and their height standard deviation (SD) scores were 0.7±0.2 SD and -3.4±0.3 SD (mean±SEM) (P<0.01), respectively. Oral glucose tolerance test (OGTT) was performed in all the subjects and GH-releasing factor (GRF) test was also performed in 13 of SO and 17 of NS. The peak levels of GH in the GRF test were significantly lower in SO than in NS (12.8±1.7 vs. 39.8±6.9ng/ml) and showed a significantly positive correlation with ∑IGFBP-1 (r=0.63, P<0.01). Serum GHBP level and IGF-I level were significantly higher in SO than in NS on pubertal stage matching. There was a positive correlation between GHBP and ∑insulin during OGTT (r=0.75, P<0.01). When the sum of the values during OGTT was expressed as ∑, ∑insulin, ∑C-peptide and glucose were significantly higher in SO than in NS on pubertal stage matching. Basal and ∑IGFBP-1 were significantly lower in SO than in NS, but IGFBP-3 levels showed no significant difference between the two groups either in prepuberty or midpuberty. In conclusion, it can be hypothesized that the overnutrition causes hyperinsulinemia which increases GH receptor and IGF-I secretion despite low GH secretion. Hyperinsulinemia also may increase free IGF-I by lowering IGFBP-1. These two mechanism are supposed to be the nutrition related hormonal changes in SO and can explain the growth of SO. In addition, the increased free IGF-I may contribute the decreased GH secretion due to negative feedback in SO.