Long-term changes in the dentoskeletal pattern in a 6-year-old Japanese girl with Beckwith-Wiedemann syndrome were demonstrated. The patient showed macroglossia, which is the most common symptom of the syndrome, protruded lower lip, mandibular protrusion and anterior open bite. The jaw base relationship improved to skeletal Class I and the molar relationship to Angle Class I at the early preadolescent period following tongue reduction and phase I orthodontic treatment using a chin cap and tongue crib. Optimum intercuspation of teeth was achieved after edgewise treatment without orthognathic surgery, and a skeletal Class I apical base relationship and good facial profile were maintained after the retention period of 2 years. This case report suggests that early orthodontic treatment with tongue reduction can be effective in a case with Beckwith-Wiedemann syndrome to improve an abnormal dentoskeletal pattern.