Low birth weight (LBW) (<2500 gm) is an important public health problem in both developed and developing countries. It adversely affects normal renal development, with sequel of expression of renal diseases after exposure to potentially injurious renal stimuli (long or short term).The aim of this work is to determine percentage of LBW cases admitted in our NICU in Kasr El-Aini Hospital, Cairo University, and study the relation of the degree of prematurity and growth restriction to kidney impairment, the relation of perinatal events and possible complications to renal affection in LBW. This study was carried out over a period of one year from 1/11/2005 to 31/10/2006.The prevalence of renal impairment was 55 % in LBW, 36 %in VLBW and 9 % in ELBW babies (in 111 babies with renal impairment). Four (6.6 %) neonates who had normal kidney function on 3rd day of age developed renal impairment by the 7th day of age. While 49.4% who had impaired kidney function on 3rd day of age showed normal function on 7th day of age. This result was statistically significant (p=0.0001).The prevalence of renal impairment in babies of mothers with pregnancy-induced hypertension (PIH) was 50.8%, which was significantly higher than that in cases with other complications of pregnancy.One hundred and thirty two (65.7%) babies were discharged alive and out of them 9.3% had impaired kidney function for follow up.