Impaired renal development during foetal life is a proposed mechanism for adult hypertension in people born small. Whether preterm birth contributes to such adverse development is still unclear. We investigated the selective contributions from foetal growth restriction or preterm birth to renal function and volume in children with low birth weight. Three groups of 9 to 12-year-old children were studied: those born at < 32 gestational weeks (preterm, n = 39), those born at term but small for gestational age (SGA, n = 29) and those born at the term appropriate for gestational age (controls, n = 37). We estimated renal function by calculating glomerular filtration rate (GFR) and by measuring urinary proteins. Volumetric ultrasound of the kidneys was performed in 86 children (preterm, n = 33; SGA, n = 25; controls, n = 29). Estimated glomerular filtration rate (eGFR) and urinary protein patterns were similar between the groups. Kidney volume (preterm 162 ml (31); SGA 163 ml (26) and controls 182 ml (47)) was smaller in the preterm group than in the controls, but the difference was not significant when adjusted for body surface area, gender and age (P = 0.25). Total renal volume correlated to birth weight (r = 0.23, P = 0.03). No significant differences were found in renal function or volume between the three groups at school age.