We have discovered a new Italian pedigree with autosomal-dominant ALS. The pedigree, at present, comprises 75 members distributed in five generations. ALS was diagnosed in eight patients. The mean ± SD age of onset of the disease was 46.8 ± 13.5 years, with a range of 29 to 63 years. The mean ± SD duration of the disease was 11.6 ± 1.7 months. Molecular genetic studies showed a missense mutation (Gly→Ser, codon 41) in exon 2 of the Cu/Zn superoxide dismutase gene (SOD1) on chromosome 21 in the available affected member and in 45% of the at-risk subjects of the pedigree. This study confirms the presence of SOD1 point mutations in families with autosomal-dominant ALS and suggests that additional genetic or environmental factors may be involved in the full expression of the disease.