Hemifacial/Craniofacial microsomia is characterised by underdevelopment of the soft tissues and bones on one side of the face.

Whilst the ear, mouth and lower jaw (mandible) are both frequently affected, the cheek, eye, skull, nerves of the face and soft tissues can be involved to varying degrees.

In 10% of cases there may be bilateral involvement, usually asymmetric.

Hemifacial/Craniofacial microsomia is non-progressive, so that the areas of the face involved early in life remain similarly affected throughout facial development, i.e. there is no deterioration or improvement.