The Department of Defense denied security clearances to 8,065 individuals in 2008, according to a recent congressional hearing volume. “These numbers represent a small percentage of the total number of security clearance investigations. The vast majority of investigations are adjudicated favorably.” See “Security Clearance Reform: Moving Forward on Modernization,” Senate Homeland Security and Governmental Affairs Committee, September 15, 2009 (published April 2010). (Update: The statistics on clearance denials are given on page 92 of the PDF version of the hearing.)
Among other recently published congressional hearing volumes on national security topics are these:
“An Uneasy Relationship: U.S. Reliance on Private Security Firms in Overseas Operations” (pdf), Senate Homeland Security and Governmental Affairs Committee, February 27, 2008 (published March 2010).
“Reauthorizing the USA PATRIOT Act: Ensuring Liberty,” Senate Judiciary Committee, September 23, 2009 (published April 2010).
“A Strategic and Economic Review of Aerospace Exports” (pdf), House Foreign Affairs Committee, December 9, 2009 (published April 2010).