Run Over @ 20,000'

[Red Air Rambo]

All kidding aside, Mid-airs can happen at any altitude...I almost had one with a couple F-15E's in Eastern Turkey rejoining on the same tanker at 21,000 (you'd think with 8 eyeballs between the 2 of them somebody would be looking at something besides the tanker) and I've also almost had one with a crop duster at 100' agl on a lowlevel. I've had numerous close calls in restricted areas and MOA's where people just fly through them VFR not talking to anybody. I always fly IFR or VFR flight following but there are people out there that fly without talking or squawking so keep your head on a swivel!