Severity of the Harlequin deformity seen in unicoronal synostosis may be augmented when frontoparietal suture synostosis has an associated fusion of the frontosphenoidal suture or in cases of isolated frontosphenoidal synostosis. The purpose of the current study is to characterize various suture fusion patterns along the coronal ring using a modified orbital index (MOI), orbital angle (OA), and endocranial base (EB) angle.This study is a retrospective single institution cohort study. Charts were reviewed over the past 12 years; patients with isolated UCS were included. MOI, OA, and EB were used to identify 3 groups of UCS patients.Twenty-one patients were identified for inclusion in skeletal dysmorphology analysis using MOI, OA, and EB measures. Frontoparietal synostosis patients were diagnosed at significantly younger ages than frontoparietal + frontosphenoidal patients (P = 0.0001). Ipsilateral MOI measures were more severe for frontoparietal patients compared with frontoparietal + frontosphenoidal patients (P = 0.0239). There was a trend for more severe ipsilateral OA measures in frontoparietal patients compared with frontoparietal + frontosphenoidal patients (P = 0.181).Modified orbital index, OA, and EB measurements are useful in the diagnosis of suture fusion patterns in UCS patients. Frontoparietal synostosis has more severe Harlequin deformity compared with frontoparietal + frontosphenoidal patients. Frontosphenoidal fusion coinciding with frontoparietal synostosis may blunt the severity of skeletal dysmorphology in UCS patients and be associated with a delayed diagnosis. Attention must be paid to assessing the frontosphenoidal suture to assure adequate surgical release.