Prenatal growth is known to affect glomerular function in adult life. It is unknown, however, whether this association is also present in children. In a cross-sectional study, we examined whether birth weight (BW) is associated with serum creatinine (measured by an improved Jaffe method) and GFR (estimated by the Haycock-Schwartz formula; eGFR) in 73 apparently healthy school-age children (35 boys and 38 girls; age 9.5 +/- 0.4 yr). All children were born after singleton term pregnancies (gestational age 39.6 +/- 0.2 wk) with normal BW (3.2 +/- 0.04 kg). A significant decrease in serum creatinine and increase in the eGFR was evident by tertiles of BW-SD score (SDS) (p = 0.001 and p < 0.0001). eGFR was correlated with BW-SDS (r = 0.45; p < 0.0001), so that each unit increase in BW-SDS was associated with an increase in eGFR of 10 (95% CI 5-14) ml/min per 1.73 m. In summary, estimates of glomerular function are in apparently healthy school-age children influenced by size at birth. These findings suggest early effects for the prenatal programming of renal function in humans.