The country's four biggest insurance companies, Aetna, Humana, WellPoint and United Healthcare, denied coverage to 1 in 7 applicants because of a preexisting medical condition from 2007-2009.  651,000 individuals were denied medical insurance in this time period by these companies according to a Congressional investigation and report. 

Source:  Wall Street Journal

The report to the House Committee on Energy and Commerce was released by Rep. Henry Waxman of California, the Committee Chair, and Rep. Bart Stupak of Michigan and can be read here.