The outcome of motor neuron disease (MND) in Japan was analyzed using questionnaires based on 768 cases. There was a significant relationship between duration of disease and age at onset, type of disease, degree of hyperreflexia, and cerebrospinal fluid protein level. The sex of the patients appeared to be related to the mode of progression in MND cases with more than 5 years of survival, although overall survival curves were similar for males and females. Geographic factors had no effect on prognosis.