The purpose of this investigation was to determine the effect of the use of valproate (VPA) on bleeding and requirement for replacement blood products in patients undergoing major surgical procedures. One hundred thirty-nine patients had posterior spinal fusion performed by 1 of 3 surgeons at our institution from 1987 to 1993. The clinical status of the patient, pre- and postoperative laboratory values, type and extent of instrumentation, surgeon performing the procedure, and medications (including VPA) were variables considered. The outcome measures were intra- and postoperative blood loss and number of blood products used. Intraoperative blood loss was correlated with the method of instrumentation, platelet count, and the surgeon performing the procedure. Postoperative blood loss was correlated with the diagnosis of cerebral palsy. By hierachical stepwise regression analysis, the only outcome measure correlated with VPA was the number of blood products used.