Patients with myotonic dystrophy (DM1) rarely complain of dyspnea despite of severe hypoxemia. We studied the perception of dyspnea caused by breath-holding in 9 DM1 patients and 8 healthy control subjects. The patients, as well as the control subjects, complained of dyspnea and showed decrease in SpO2. In none of the patients but one, however, the bottom SpO2 became lower than the minimal SpO2 recorded in 24-hour monitoring. DM1 patients were able to realize hypoxia caused by apnea, although they had not realized hypoxia that already existed. Consequently, the breath-holding test does not uncover a blunted perception of dyspnea in DM1; an afferent system contributable to air hunger sensation in breath-holding is preserved in DM1. Breath-holding test may be useful for a DM1 patient to recognize the significance of sleep apnea.