The kidney of low birthweight preterm infants is characterized by a reduced number of mature nephrons at birth. The aim of the present study was to determine whether, in preterms, active glomerulogenesis occurs in the postnatal period and whether it may compensate the reduced number of nephrons developed during the intrauterine life. Kidney samples were obtained at autopsy from 8 human fetuses, 12 premature infants, and 3 term newborns. Glomerulogenesis, as measured by radial glomerular count (RGC), was markedly decreased in all preterm infants as compared with term newborns. A marked interindividual variability was detected in the level of glomerulogenesis, which, in the vast majority of cases, did neither correlate with the gestational age at birth nor with birthweight. Active glomerulogenesis, as demonstrated by the presence of S-shaped bodies in the subcapsular region, was present in all preterm infants in the perinatal period, but it ceased in a preterm surviving for 3 months. Our data show that active glomerulogenesis continues even after birth for a short period, although it is not able to compensate a marked oligonephronia at birth. As a consequence, the incomplete nephrogenesis typical of all extremely low birthweight preterm infants possibly results in a persistent oligonephronia which should likelihood represent a major risk factors of progressive renal disease in adulthood.