Name, location No. of physicians Year founded
Mayo Clinic 1,071 1890
Henry Ford Medical Group 1,000 1915
Lahey/Hitchcock 830 Lahey 1923; Hitchcock 1927
Burlington, Mass., and Lebanon, N.H.
Cleveland Clinic 600 1921
Geisinger Clinic 529 1915
The list doesn't include prepaid medical groups such as Kaiser Permanente in California, with 3,562 physicians, and Southern California Permanente, with more than 2,000. It also excludes university faculty practice plans.
Sources: American Group Practice Association and Medical Group Management Association membership lists; staff research