Some types of background and security checks return results within a few days and do not significantly prolong USCIS processing times or hinder backlog reduction goals. However, while the overall percentage of long-pending cases is small, as of May 2006, USCIS reported 235,802 FBI name checks pending, with approximately 65 percent (153,166) of those cases pending more than 90 days and approximately 35 percent (82,824) pending more than one year.
Details in :
http://www.dhs.gov/interweb/assetli...Name_Checks.pdf