Eight years after the first description of mitochondrial DNA mutations in neuromuscular syndromes, the relatively unknown field of mitochondrial disorders has become a major topic not only in neurology, but in various other fields of medicine. Dozens of mitochondrial DNA mutations have been associated with neuromuscular, ophthalmologic, endocrinologic, gastrointestinal, and even psychiatric disorders. In addition, potentially pathogenic mutations in mitochondrial DNA have also been identified in normal aging and age-related neurodegenerative disorders. Despite the wealth of information and insights gathered, treatment is still tentative.