THE ESTABLISHMENT ON the upper Mississippi River of the Mayo Clinic, the earliest example of group surgical practice in the United States, was a seminal event in the evolution of American surgery. By the early 1890s, the two brothers William James Mayo (1861-1939) and Charles Horace Mayo (1865-1939) were completing hundreds of surgical operations a year. The growth of the Mayos' surgical practice was simply phenomenal, and by the turn of the 20th century, the numbers were up to almost 3000 procedures annually. Virtually free of competition or political interference, the Mayos established not only an international reputation but also a private multispecialty clinic that was to become a trademark of American medicine. In 1897, the brothers began to hire interns at their hospital. Physicians also came to observe the Mayos at work, and these visits were soon organized into formal courses in graduate surgery. The clinic grew rapidly, and by 1907 almost 7500 patients yearly, of whom 5000 were surgical, were being treated. In 1915, having accumulated a substantial fortune, the Mayos gave $1.5 million to endow the Mayo Foundation for Medical Education and Research in affiliation with the graduate school of the University of Minnesota. Thus, the Mayo Clinic provided one of the first degree programs in graduate medical education and became a center for surgical training.