Hemifacial microsomia (HFM) is the most common congenital facial anomaly except cleft lip and palate, which involves maldevelopment of craniofacial bones, muscles, soft tissues, facial nerves, auricles and extracranial organs. The disease affects unilaterally more frequently than bilaterally. The exact etiology and pathogenesis are still unclear. The reported pathogenesis includes genetics, environment and the mutual reaction. In this paper, the etiological investigations of HFM were classified and reviewed.