Mutations in the SOD1 gene exons and exon/intron boundaries were searched in 66 sporadic and 4 familial Italian ALS cases consecutively referred to our centre from different Italian regions. A mutation was found in three sporadic cases (4.5%): a new nonsense mutation in exon 5 (K136X) in a patient with a rapid and severe disease course and two previously described missense nucleotide substitutions (N65S and A95T) in two patients with a mild disease course. Comparison of the clinical characteristics with previously reported patients carrying the same or similar mutations showed a remarkable genotype-phenotype correlation. No association was found with intronic sequence variations by comparing their frequency in the patients and in 181 matched controls.