Objective: To describe the phenotypic and genotypic features of two unrelated Italian amyotrophic lateral sclerosis (ALS) patients, a FALS case and an apparently sporadic case, carrying the same D124G SOD1 mutation. Since this mutation is very rare, previously reported in only one patient of unknown geographical origin, to look for a founder effect. Methods: Cases were classified based on the El Escorial revised criteria. Genomic DNA was isolated from whole blood samples and the coding region of the SOD1 gene was analyzed by polymerase chain reaction (PCR) and sequencing. For the haplotype analysis, genotyping was carried out using eight polymorphic markers flanking the SOD1 gene. Results: Both patients had a spinal onset in the lower limbs and progressive muscular atrophy (PMA) phenotype. The progression of the disease in our cases differed from that reported for PMA patients, characterized by a longer survival than the majority of ALS phenotypes, being more aggressive, in particular in the sporadic case (survival less than 1 year). Genotyping showed a shared haplotype for the D124G allele and the estimate of the mutation dating revealed that the mutation originated approximately 400 years ago. Conclusions: We have defined for the first time the clinical profile associated with the D124G mutation in SOD1 gene and provided evidence that this mutation in Italy originates from a common founder.