What are the largest health insurance companies in the US?

The following health insurance companies/managed care organizations are shown with their overall Fortune 500 ranking as a US company (2008): 1. UnitedHealth Group - 25 2. WellPoint - 33 3. Aetna - 85 4. Humana - 98 5. Cigna - 141 6. Health Net - 179 7. Coventry Health Care - 266 8. Amerigroup - 555 9. Universal American - 669 10. Centene - 685