What does an FBI backround check show?

Answer 1

Everything; the FBI has arguably the most exhaustive and extensive BI processes in the government.

Assuming you pass the Bureau's stringent polygraph test (high pucker factor, high failure rate, not given until you pass the first interviews), the BI you'll go through is extensive and thorough.

The Bureau will conduct extensive records checks on your history (everything from legal, military, education, financial, employment, medical, etc.). They'll also interview people from your life (family, friends and neighbors (current and past, from every place you ever lived), coworkers (current and former), ex-spouses, pastors/priests, you name it, will be interviewed by current or former agents to determine a background profile. That includes any place you may have lived outside the U.S., or any foreign friends you may have had or still have.

Expect them to review at least as far back as 20 years if you've never had a clearance; having a military or other government agency BI and clearance is helpful, but they'll still do their own BI.