I have quite a few friends and relatives with security clearances, so although I haven't gone through the background check myself, I think I'm qualified to talk about it in general terms. This is all secondhand, of course. They're looking for levers that outside folks could use to manipulate you. As long as you're not especially susceptible to bribery (i.e., not in massive debt, no current drug addictions, not a compulsive gambler, etc) and have no skeletons in your closet that someone could use for blackmail, I would expect you to pass easily. If anyone I know ever failed a government background check, they didn't tell me about it. One person has told me that the process involves an interrogation that's several hours long and extremely unpleasant. jkaufman is a LWer who had (has?) a clearance, and he's a helpful guy (and also one of my sources for the above). You could PM him if you want to talk to someone who actually went through the process.