: Familial amyotrophic lateral sclerosis (ALS) are caused by the mutations in the copper (Cu) / zinc (Zn) superoxide dismutase 1 (SOD1) gene. SOD1 has been reported to play a critical role in glucose metabolism in yeast and cell models, and mice. However, effects of SOD1 for glucose metabolism in humans remain unknown. A 72-year-old woman was admitted to our hospital due to hyperglycemia. She showed severe muscle atrophy and visceral fat accumulation due to ALS. Her serum free fatty acids levels elevated and serum Cu and Zn levels decreased. Her two younger brothers and aunt were also diagnosed as having ALS, and DNA sequence analysis revealed the presence of the I113T SOD1 mutation. She may have developed diabetes due to SOD1 dysfunction by the I113T SOD1 mutation, and severe insulin resistance induced by ALS. The I113T SOD1 mutation may be the causative factor for diabetes as well as familial ALS.