They absolutely do! I didn't realize just how big of an impact a silly video game could have. When my lot became old enough to play them I could tell you who played what by their behavior after and during their playing time. My son is a nice kid, but when he plays the violent games, another side of him comes out, this only happens when he plays the games. He is easily irritated, short with his siblings and generally disagreable. The effects of playing a game ie: aggression, irritability, etc., don't last long. Once they are away from it for a couple of hours they tend to go back to their regular personality. I don't know what kind of long term affects they may have, there must be some, that's why I ban some of the games from our home.