We report the clinical and neuropathological features of a Japanese family with familial amyotrophic lateral sclerosis (FALS), whose members have an amino acid substitution of histidine by arginine in Cu/Zn superoxide dismutase. A 58-year-old woman developed muscle weakness in the legs, and died of respiratory insufficiency 7 months after the onset of her weakness. Her family history included 7 patients with FALS over 3 generations. Their pertinent neurological abnormalities consisted primarily of lower motor neuron signs, and their clinical progression was rapid. Autopsy of our patient showed the involvement of the lower and upper motor neuron systems with Lewy body-like hyaline inclusions, in addition to degeneration in the posterior columns, Clarke's nuclei and posterior spinocerebellar tracts. The inclusions reacted with both anti-SOD1 and anti-ubiquitin antibodies. This is the first report of the neuropathological findings of FALS with this mutation.