After a substantial review of the current research the American Psychological Association had determined that the research suggests a link between playing violent video games and increased aggression. No link was found between playing such games and criminal violence and aggression. They stated that it may not be as simple as playing violent games leading to aggression. It is more likely that playing such games is one of several risk factors that can lead to increased aggression, especially if more than one of those risk factors is sufficiently combined.
The APA recommended that violence in games be reduced overall, and that video game companies develop a more informed and accurate rating system for the games.
http://www.apa.org/news/press/releases/2015/08/violent-video-games.aspx
http://www.apa.org/news/press/releases/2005/08/video-violence.aspx
