Death is the most important end point along the course of amyotrophic lateral sclerosis (ALS). It is commonly attributed to a respiratory failure in relation with a restrictive respiratory disorder. However, in clinical practice, it is frequent to observe that death has not direct relation with the values of the respiratory function, at least measured with vital capacity. It is also frequent that relatives report sudden death during nocturnal sleep. All these features raised the question of the possible relation between death and nocturnal oxymetry in ALS patients. In a prospective study, we studied 69 ALS patients. We recorded demographic data, clinical parameters as manual muscle testing and functional scales, various parameters of oxymetry measured by pulse oxymetry recorded during night, slow vital capacity and survival time. There is a strong correlation between survival time measured by Kaplan Meier curves and log rank and the mean nocturnal saturation. We determined 93 mmHg as a threshold value. Below this threshold, mean survival time was 7.5+/-1.6 months and above it was equal to 18.5+/-1.5; relative risk was 3.31. These data confirm the importance of nocturnal oxymetry on survival in ALS patients both in clinical practice and in view of therapeutic trials.