Mayo Clinic is a not-for-profit medical practice and medical research group based in Rochester, Minnesota. It is the first and largest integrated not-for-profit medical group practice in the world, employing more than 3,800 physicians and scientists and 50,900 allied health staff. The practice specializes in treating difficult cases through tertiary care. It spends over $500 million a year on research. Mayo Clinic has been near the top of the U.S.