Rapid infancy weight gain is associated with subsequent higher circulating insulin-like growth factor (IGF) I levels in normal children. We hypothesized that circulating levels of growth hormone binding protein (GHBP), a putative marker of GH sensitivity, may also be associated with postnatal weight gain and insulin secretion. In 751 normal children aged 7 to 8 years, we measured insulin, glucose, GHBP, IGF-I, IGF binding protein (IGFBP) 1, and IGFBP-3 levels in a fasting venous blood sample. Insulin secretion was assessed by measuring insulin and glucose levels 30 minutes after an oral glucose load. After adjustment for current weight, birth weight was inversely related to IGF-I and GHBP levels. Children with lower birth weight and rapid weight gain between birth and 3 years had higher IGF-I and GHBP levels and also lower IGFBP-1 levels than other children. Allowing for current body mass index, GHBP levels were positively related to insulin secretion. In conclusion, children who showed rapid early postnatal weight gain after low birth weight have higher levels of GHBP than other children. Increased GH sensitivity in such children could contribute to links between rapid infancy weight gain and subsequent faster rates of childhood growth and maturation.