We aimed to assess whether patients with hemifacial microsomia can be quantitatively identified using bone mineral density information. Mandibular bone mineral density was studied using computer assisted analysis between the nonaffected (r) and the affected (l) sides with an orthopantomograph in a patient with hemifacial microsomia with median mandibular cleft, and four patients who suffered from hemifacial microsomia in the left side. Fifty controls without bone diseases were randomly selected. Bone mineral density r/l ratios in the controls ranged from 0.479 to 2.064, and those in two patients that were associated with and without median mandibular cleft were higher than those in the controls, with a maximum of 8.622 in a particular male with median mandibular cleft after bone graft, whereas the r/l ratios in the other three cases were similar to the controls. Our findings indicate that the quantitative character in the case with median mandibular cleft reveals a large discrepancy of bone mineral density between the nonaffected and the affected sides. This may suggest a compensatory mechanism for bone hypertrophy from regulated bone mineral density with underdevelopment in hemifacial microsomia.