I think I've seen 5 UFOs in a span of three months five years ago.  At first I thought "It's just some plane or something..." but planes are usually loud and you can hear them. What I saw was completely silent.  A friend of mine said, "Maybe it was one of those stealth jets used by the Military?"  I considered the thought, then I replied to him, "Yeah, but how many stealth jets fly at night with red, blue, and green lights? Not very 'stealthy' now is it?"  I still don't know what I saw...

Anyway, the Universe is large so there is a possibility that they do exist.