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Aims: To assess postnatal kidney volume development and to compare the intrauterine and extrauterine kidney growth curves of premature infants. Methods: One hundred neonates were enrolled in this study, and all infants had their kidney volumes measured by renal ultrasound examination. Group GA consisted of 44 neonates who were evaluated within 48 h after birth, and their gestational ages were used in the analysis. Group CA included 56 premature infants born before 34 weeks of gestation and was evaluated 14–96 days after birth, and their conceptional ages were used in the analysis. Left kidney volume, body weight, body height and age were used in the correlation analysis. Results: There was a better kidney growth rate for Group GA infants than for Group CA infants ( P = 0.001). Kidney volumes in Group CA infants were thus apparently larger than those of the Group GA infants before 31 weeks of age, but they were smaller after 31 weeks of age. Group GA infants had a significantly faster growth in body weight ( P = 0.001) and body height ( P < 0.001). However, a larger kidney volume was noted in Group CA infants with the same body weight ( P < 0.001). Conclusion: A chart is presented of the postnatal growth of normal kidney volume before 40 weeks conceptional age in premature infants. These data suggest that intrauterine growth may have a regulatory influence on kidney growth, and the reduced kidney volume in premature infants may result from the early extrauterine period. [ABSTRACT FROM AUTHOR]