Valproic acid (VPA) is used in the treatment of seizure disorders often present in patients with cerebral palsy. The charts of 114 patients with cerebral palsy were reviewed to evaluate the effect of VPA on blood loss during spine surgery. Forty-one patients had seizure disorders. Of these, 18 were taking VPA as monotherapy (group III) and the remaining 23 patients were taking other antiseizure medications, including two taking VPA (group II). There was a significant increase in the number of patients with abnormal bleeding times and a significant difference (p < 0.001) in blood loss (ml/kg) in patients taking VPA as monotherapy (38.6 ml/kg vs. 30.0 ml/kg). There was also increased blood-product administration postoperatively in the VPA monotherapy patients. Physicians should be aware of this potential association between VPA use and increased blood loss. The routine laboratory tests of complete blood count, prothrombin time, and partial thromboplastin time will not adequately screen for the platelet-mediated effects of VPA.