Background: Preoperative severity and postoperative success for patients with sagittal synostosis are measured by cephalic index, but this metric does not describe the appropriateness of euryon location. The authors hypothesize that cephalic index in patients with sagittal synostosis is an inaccurate measure of scaphocephaly. Methods: Preoperative and 1-year postoperative cranial computed tomographic scans of children with sagittal synostosis treated before 6 months of age by either total calvarial reconstruction or endoscope-assisted craniectomy and helmet therapy (n = 10 for each) were reviewed retrospectively. The location of euryons in age-matched controls was measured as a fraction of the glabella-opisthocranion distance (horizontal point of maximum width) and as the fraction of the nasion-vertex vertical distance (vertical point of maximum width). Cephalic index at this ideal location (normative cephalic index) and traditional cephalic index were determined in all patients. Results: Ideal euryon location from preoperative controls was 56 percent by the horizontal point of maximum width and 56 percent by the vertical point of maximum width. Normative cephalic index (0.60) was significantly less than traditional cephalic index (0.66) in patients preoperatively (p < 0.001) and remained smaller postoperatively (0.68 versus 0.73) for patients who underwent open reconstruction (p < 0.001). Patients treated endoscopically also had a smaller normative cephalic index (0.71) than traditional cephalic index (0.76) postoperatively (p < 0.001). Conclusions: Anterocaudal displacement of euryon in patients with sagittal synostosis influences cephalic index. Normative cephalic index, assessed at ideal euryon location, is a more accurate measure of preoperative severity and postoperative outcome.