Of all the SOD1 gene mutations described, uniquely the D90A mutation has been identified in recessive, dominant, and apparently sporadic cases. We describe a patient with a sporadic form of amyotrophic lateral sclerosis (ALS) in which a heterozygous A > C exchange at position 272 in the SOD1 gene was detected. This mutation results in an amino acid substitution of alanine for aspartate at position 90 (D90A). The patient had a 12-year history of disease characterized by slow progression. Clinical examination at last follow-up revealed predominant upper motor neuron (p-UMN) involvement, with atrophies only in distal muscle of upper limbs. Electrophysiological examination revealed lower and upper motor neuron involvement. Family history was negative for neurological disease. This report shows that D90A in heterozygous state may cause p-UMN phenotype with very slow progression.