A 72-year-old, seemingly healthy, Japanese man suddenly lost consciousness. At the emergency room, the patient's Glasgow coma scale score was 10 and a thoracic breathing pattern was observed. An arterial blood gas analysis indicated acute hypercarbic respiratory failure. He was placed on non-invasive positive pressure ventilation. The next day he was alert. Manual muscle testing revealed that his face, neck and limb muscle strength were normal. He could walk, and Gowers' sign was not observed. Computed tomography showed atrophy of the paravertebral, abdominal wall and diaphragm crura muscles, without apparent limb muscle involvement. Pompe's disease was diagnosed based on the results of biochemical and genetic tests for acid alpha-glucosidase.