Myasthenia gravis is a nerve-muscle junction disease, for which the most specific test is an increase in the anti-acetylcholine receptor antibodies (anti-AChR-Abs) titer. Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting both upper and lower motor neurons. Positive AChR-Ab in patients with pure ALS are exceedingly rare. We report the case of a patient with confirmed ALS and very high levels of AChR-Ab and review the literature on this topic.