The aim of our study is to better understand the maxillary involvement in relation to the mandibular deformation in hemifacial microsomia (HFM). To do so, consecutive patients with HFM treated at The Children's Hospital of Philadelphia from 2000 to 2012 were included in our study. Both two-dimensional and three-dimensional analyses of the bony and sinus structures of the midface and mandible were performed using three-dimensional segmentation software. Patients were stratified into groups based on the Kaban-Pruzansky classification--mild (0-1), moderate (2A), and severe (2B-3)--as well as rank ordering based on overall severity. Analyses involved paired t-tests within severity groups, 1-way analysis of variance when assessing across groups (ipsilateral/contralateral ratio), and regression to assess for trends. Thirty patients were included (4 mild, 12 moderate, and 14 severe). The mandibular volume ratio differed across all patient groups (P < 0.001) and trended with rank order (P < 0.001). No significant difference in maxillary bony volume ratio was found across all patient groups (P = 0.16). In patients with severe disease, the maxillary bone volume was found to be significantly decreased on the ipsilateral side as compared with the contralateral side (P = 0.0123). There was no difference in maxillary sinus volume between ipsilateral and contralateral sides within any patient groups or in comparing across groups (P = 0.10). No significant trend was found in the volume ratio of mandible and maxilla (P = 0.41). To conclude, the maxillary sinus seems to show no difference in volume when comparing between laterality and severity groupings. These findings suggest that there may be alternative influences other than the vascular insult acting as the driving force behind the mandibular deformity and the additional classic clinical findings of HFM.