The single biggest risk factor for the vast majority of chronic diseases is old age. For many diseases, in fact, a person's birth date is a larger red flag than all other known risk factors combined. But for too long, physicians thought that the aging process was impossible to modify or slow down. Like death and taxes, growing old—and the medical problems that come with it—was considered inevitable. That's starting to change. In this special news focus on aging, Nature Medicine looks at the progress being made in drug interventions for the elderly and the hurdles that remain in the pursuit of a pharmaceutical elixir for healthy aging.