A 56-year-woman with type 2 respiratory failure due to diaphragmatic dysfunction in Charcot-Marie-Tooth disease (CMT) is reported. The patient, who had a 50-year history of CMT, was referred to our hospital because of nocturnal dyspnea. Arterial blood gas analysis on admission showed marked hypoxia with hypercapnia, and physical examination revealed thoracoabdominal paradoxus in the supine position. Chest radiography revealed elevation of both sides of the diaphragm. The vital capacity and arterial blood gas pressure in the sitting position were markedly higher than those in the supine position. Electrical phrenic nerve stimulation failed to produce any convincing muscle action potential in the diaphragm. These findings suggested that her respiratory failure was induced by both diaphragmatic dysfunction caused by bilateral phrenic nerve palsy due to CMT. Treatment of this patient was started at home with a pressure support ventilator, resulting in satisfactory clinical improvement. In general, respiratory muscle impairment is a rare phenomenon in a patient with CMT. However when a patient with CMT complains of dyspnea or if unexpected heart failure develops, it is important to keep in mind that CMT may be associated with phrenic nerve palsy.