Only few cases with REM sleep behavior disorder (RBD) have been previously reported in amyotrophic lateral sclerosis (ALS). It is unknown if ALS per se impairs sleep motor function, besides respiration. Rapid eye movement (REM) sleep without atonia (RSWA) was found to be frequent in ALS patients without RBD. RSWA without RBD correlates with ALS severity. The mechanisms by which ALS pathology causes RSWA may be multiple and complex.