Valproic acid (VPA) may increase surgical bleeding. The purpose of this study was to review the effect of VPA on blood loss during bilateral femoral osteotomy in children with cerebral palsy. The medical records of 29 children were retrospectively reviewed. Blood volume, total blood loss, and postoperative blood loss were calculated. Fourteen children were taking no anticonvulsant medications, nine children were taking anticonvulsant medications other than VPA, and six children were taking anticonvulsant medications including VPA. The group taking anticonvulsant medications including VPA had significantly lower preoperative platelet counts (204,000) and a significantly greater incidence of transfusion (50%). Compared with the group taking no anticonvulsant medications, the group taking anticonvulsant medications including VPA had a significantly greater change in hematocrit and greater blood loss. Blood loss and the need for transfusion should be anticipated for in children with cerebral palsy taking VPA who undergo femoral osteotomy.