Left handed, I've always used my mouse with my right hand, and otherwise play right-handed. I've tried using a mouse with my left hand and I can't at all. Everything else I do left handed, write, throw, swing, stand on a board, but gaming I learned it right handed I guess. I don't know, someone put me in front of a computer, the mouse was on the right, so I grabbed it with my right hand, it just made sense and worked for whatever reason.