Neurodegeneration in amyotrophic lateral sclerosis (ALS) is characterized by the specific loss of central and peripheral motor neurons. While this pattern of neuronal demise gives rise to a distinct clinical syndrome, at the cellular and molecular level ALS pathology is similar to that seen in other neurodegenerative diseases. In particular, mitochondrial dysfunction in ALS is reminiscent of that observed in Alzheimer's and Parkinson's diseases. Mitochondria in persons with ALS demonstrate impaired electron transport, increased free radical generation, and an inability to adequately buffer cytosolic calcium shifts. These abnormalities are probably systemic and potentially due to mutation of mitochondrial DNA.