The aim of this study is to determine whether or not renal involvement was present during the early neonatal period in preterm infants with PVL. We conducted a case-control study. The following items were evaluated; urine output, serum levels of sodium (Na), potassium (K), chloride (Cl), urea nitrogen (UN), and creatinine (Cr). The factors that could influence the urine output were also compared between the PVL and the control group. The mean urine output during the first 24h in the PVL group was 19.8ml/kg/day, and was significantly lower than in the control group (28.8ml/kg/day, p<0.05). The mean UN and Cr were not significantly different between the two groups. The minimal serum Na and Cl levels in the PVL group were significantly lower (128.3 and 94.3mEq/l) than those in the control group (134.8 and 100.7mEq/l, p<0.01 each). The maximal serum K level was significantly higher in the PVL group (6.47mEq/l) as compared to the control group (5.57mEq/l, p<0.05). There were no differences in any postnatal variables between the two groups. The preterm infants who later developed PVL had mild but significant oliguria during the first 24h of life. This suggests that preterm infants with PVL will have renal involvement immediately after birth.