Mutations in mitochondrial DNA cause a group of diverse diseases that affect an estimated half a million people worldwide. These disorders are remarkably resistant to conventional treatments, and thus several gene therapy approaches are being explored. As some of these approaches develop towards maturity, one can't help thinking that some day they may be used against a much more common health problem currently affecting about 6 billion people— aging, which also has been quite resistant to treatment. Unfortunately, we still do not know whether mtDNA mutations significantly contribute to the aging process or not. The prospect of success in mtDNA gene therapy makes getting the answer a high priority.