A family is reported in which three out of four siblings of a consanguineous healthy couple developed adult onset Amyotrophic Lateral Sclerosis (ALS). All patients showed a similar clinical course with regard to disease progression and absence of cognitive deterioration. Laboratory findings included modification of Spinal Evoked Potential (SEP) and normal value of thiamine and thiamine monophosphate in cerebrospinal fluid (CSF). These data suggest an autosomal recessive mode of inheritance of ASL in this family.