The features of hemifacial microsomia with unilateral condylar hypoplasia in a 9-year-old female patient were analysed in a multidisciplinary fashion. Cephalometric roentgenograms revealed malformation of the mandible, with the right condylar process being smaller than the left. In addition, the right maxillary alveolar process was underdeveloped. Closed view radiography with oblique lateral transcranial projection (by modified Schüller's method) of the temporomandibular joint revealed an anterior dislocation of the condyle on the unaffected side. Computed tomography (CT) of the masticatory muscles demonstrated that the medial pterygoid muscle on the affected side, unlike the other muscles, was larger than that on the unaffected side. The surface electromyographic activities of the temporal and masseter muscles and reduction of the maximum bite force on the affected side during clenching corresponded with the CT findings. The hypertrophy of the medial pterygoid muscle on the affected side was considered likely to be a compensatory adjustment to keep the mandible centred. A three-dimensional study of the movement of the mandible revealed that the condyle on the affected side moved vertically and that the rotational centre was located antero-inferior to the condylar process during maximum jaw opening and closing movements. These findings suggested lack of articular guidance. Moreover, the unaffected condylar process showed considerable backward movement during retrusion and ipsilateral excursion of the mandible. The mandibular head on the unaffected side showed obvious protraction during all jaw movements, which might have induced the overgrowth of the condylar head on the unaffected side in this growing child.