BACKGROUND: Most cranial vault remodeling for craniosynostosis is associated with substantial blood loss necessitating transfusion. The transfusion of over 25 ml/kg of red blood cells has long been considered an important safety threshold and has been proposed as a potential marker of health care quality, despite a lack of evidence. The authors sought to ascertain risk factors for transfusion in cranial vault remodeling and to quantify the effect of transfusion volume on postoperative complications. METHODS: Patients who underwent complex cranial vault remodeling for craniosynostosis were identified from the Pediatric National Surgical Quality Improvement Program database. Multivariate regression models were used to identify independent risk factors for transfusion and to assess its impact on subsequent outcomes. RESULTS: One thousand fifty-nine patients met inclusion criteria. Seven hundred seventy-seven patients (73.4 percent) required a transfusion and 520 patients (49.1 percent) required a transfusion in excess of 25 ml/kg. Neither transfusion nor transfusion volume in excess of 25 ml/kg had a significant effect on postoperative outcomes. Therefore, the authors sought to determine a more meaningful threshold. The top 20 percent of transfusion volumes were greater than or equal to 45.28 ml/kg. Recursive partitioning generated a threshold of 62.52 ml/kg, which independently predicted a greater number of complications and was associated with higher odds ratios than the quintile method. A threshold of 60 ml/kg was chosen for simplicity and was independently predictive of overall complications, medical complications, and increased length of stay. CONCLUSIONS: Transfusion is common in complex cranial vault remodeling. Currently described occurrence thresholds do not accurately convey postoperative risk. Transfusion in excess of 60 ml/kg significantly increases risk for complications and length of stay in cranial vault remodeling. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, III.