Intraventricular hemorrhage (IVH) is an incompletely understood complication of extremely low birthweight (ELBW) premature infants without specific treatment or preventive strategies. Although early studies suggested that serum sodium (Na) and/or sodium bicarbonate may be associated with IVH, a more recent report found no correlation. We hypothesized that early hypernatremia was present in ELBW infants with severe IVH and performed a case-control study to investigate this hypothesis. ELBW infants with severe IVH (bilaterally grade III or grade IV) treated at Evanston Hospital between 1990-1995 were compared to gestational age and birthweight matched ELBW infants with a normal cranial ultrasound over the same time period. Charts of 14 IVH patients and 14 case-controls were reviewed and data recorded including birthweight, gestational age, serum sodium maximum on day of life #1, 2, and 3, fluid intake, minimum blood pressure, minimun arterial pH, and specifics of cranial ultrasound examinations. Groups were similar in gestational age (25.3± 0.3 wks control vs 24.7 ± 0.3 wks IVH, p=NS) and birthweight(824 ±28 gm control vs 730 ± 58 gm IVH, p=NS). All IVH patients had grade IV bleeds except 4 with bilateral grade III IVH. We found that maximum serum sodium values were higher in the IVH group compared to controls at each day studied (day 1: 152 ± 3.6 meq/L IVH vs 142 ± 1.4 control, p < 0.02; day 2: 160 ± 5.0 meq/L IVH vs 149 ± 1.5 control, p < 0.03; day 3: 157 ± 1.9 meq/L IVH vs 150 ± 1.5 control, p < 0.02). Furthermore, the IVH group had a significantly higher percentage of babies with sodium values ≥ 155 meq/L compared to controls on the first days of life (day 1: 50% IVH vs 0 controls; day 2: 55% IVH vs 8% control). In addition, the IVH group had more acidosis on the first day of life (minimum pH 7.15 ±.06) compared to controls (pH 7.30 ±.02, p < 0.02), but similar acid-base balance on the second and subsequent days of life. We conclude that hypernatremia on the first few days of life is associated with severe IVH in ELBW infants. Further studies are warranted to delineate whether early hypernatremia may predispose ELBW infants to the occurrence of a significant intraventricular hemorrhage.