ALS patients supported by a ventilator often suffered from difficulty in communicating with others. We herein proposed a new classification of clinical stages of advanced ALS focusing on the degree of communication disturbance. We analyzed the relationship between clinical findings and the prognosis for communication disturbance. Twenty-nine ALS patients without dementia were enrolled in the study. The proposed classification consisted of five stages. Stage I: communicate in sentences, stage II: communicate with one word answers only, stage III: communicate with nonverbal yes/no response only, stage IV: cannot communicate occasionally due to uncertain yes/no responses, stage V: cannot communicate by any means. Clinical analysis showed that patients who reached stage V had begun to use the ventilator significantly earlier than patients with the final stages of IV or less. In addition, patients in stage V frequently had a family history of ALS. Rapid disease progression before ventilator use in patients with a family history might predict a poor long-term prognosis for communication disorder after using the ventilator.