Nephrogenesis occurs predominantly in late gestation at a time when preterm infants are already delivered. The aims of this study were to assess the effect of preterm birth and the effect of antenatal glucocorticoid treatment on nephrogenesis. Preterm baboons, which were delivered at 125 days gestation and ventilated for up to 21 days postnatally, were compared to gestational controls. A cohort of preterm baboons that had been exposed to antenatal glucocorticoids were compared to unexposed preterm baboons. The number of glomerular generations was estimated using a medullary ray glomerular counting method and glomerular number estimated using unbiased stereology. CD31 and WT-1 localisation was examined using immunohistochemistry and VEGF was localised using in situ hybridisation. The number of glomerular generations was not affected by preterm birth and total glomerular numbers were within the normal range. Kidneys were significantly enlarged in preterm baboons with a significant decrease in glomerular density (number of glomeruli per gram of kidney) in the preterm kidney as compared to gestational controls. Neonates exposed to antenatal steroids had an increased kidney-to-body weight ratio and also more developed glomeruli compared to unexposed controls. Abnormal glomeruli, with a cystic Bowman's space and shrunken glomerular tuft, were often present in the superficial renal cortex of both the steroid exposed and unexposed preterm kidneys; steroid exposure had no significant effect on the proportion of abnormal glomeruli. The proportion of abnormal glomeruli in the preterm kidneys ranged from 0.2% - 18%. In conclusion, although nephrogenesis is on-going in the extrauterine environment our findings demonstrate that preterm birth, independent of steroid-exposure, is associated with a high proportion of abnormal glomeruli in some, but not all neonatal kidneys. Whether final nephron endowment is affected in those kidneys exhibiting a high proportion of abnormal glomeruli is yet to be confirmed.