There is a paucity of reports of classic amyotrophic lateral sclerosis (ALS) developing in survivors of paralytic poliomyelitis. We describe a patient with classic ALS and an antecedent paralytic disease thought to have been poliomyelitis from which she recovered completely. If the paucity of ALS preceded by true poliomyelitis is not merely a matter of underreporting, antecedent paralytic poliomyelitis may have a protective role against the development of ALS. This has implications relevant to pathogenesis and to projected secular trends of ALS incidence since the introduction of poliomyelitis vaccines. There is a need to establish the incidence of cases of classic ALS in patients with antecedent poliomyelitis.