In 515 cases of motor neuron disease followed until death, (1) the proportion of three subtypes of motor neuron disease (MND): amyotrophic lateral sclerosis (ALS), progressive bulbar paralysis (PBP), spinal progressive muscular atrophies (SPMA) was 78.3, 1.9, 19.8; (2) sex ratios were 1.41 in ALS, nearly one in PBP and 1.59 in SPMA, the ratio being high in cases initially involving the upper limbs; (3) age at onset was smoothly unimodal and identical in three subtypes; (4) bulbar symptoms appeared either at the initial stage or towards the fatal end; (5) duration was compatible with a compound Weibull distribution; (6) survival rates showed a reverted J type distribution and was more favorable in SPMA than ALS; (7) life expectancies decreased first but increased about 46 months after onset; (8) multivariate analysis disclosed that duration is shorter in ALS when age at onset was older, and when bulbar muscles or left limbs were initially affected, and in SPMA when age at onset was older, dysphagia was present, and probably in those patients who had a history of trauma.