• Recent data suggest that early loss of brain tissue water content, ie, decreased extravascular cerebral tissue pressure, may play a role in the pathogenesis of germinal matrix/intraventricular hemorrhage in the premature newborn. This study examines the relationship between the concentration of serum sodium and germinal matrix/intraventricular hemorrhage in 299 premature infants with birth weights of less than 1500 g during the first 4 days of life. Intraventricular hemorrhage developed in 34 (32%) of the 106 infants with maximum serum sodium levels of 145 mmol/L or less and in 54 (28%) of 193 infants whose highest serum sodium levels were greater than 145 mmol/L (χ2=0.37). These data suggest that concentrations of serum sodium greater than 145 mmol/L are not associated with an increased risk of germinal matrix/intraventricular hemorrhage in the premature newborn. Consequently, more liberal administration of fluids to maintain extravascular cerebral tissue pressure is unlikely to reduce the incidence of germinal matrix hemorrhage/intraventricular hemorrhage.