Family members are often the most likely to be compatible living kidney donors, but many people undergo successful transplants with kidneys donated from people who are not related to them. Living donors will have a full medical exam, must be at least 18 years old, and in good physical and mental health. Different transplant centers have different limits on who can donate. The Kidney Transplant Learning Center offers resources on how to prepare to make the living donor ask and/or to have a family member or friend serve as a living donor champion.