Recent research reveals that playing prosocial video games increases prosocial cognitions and helpful behaviors [Gentile el al., 2009; Greitemeyer and Osswald, 2009; 2010; 2011]. These results are consistent with social-cognitive models of social behavior [e.g., the General Learning Model, Buckley and Anderson, 2006]. The social-cognitive learning models suggest that in addition to influencing cognitions, media content may also influence affect. However, past studies on prosocial video games have failed to find a significant effect on affective measures [Greitemeyer and Osswald, 2010]. The present research examined the effects of prosocial, neutral, and violent video games on state hostility and positive affect. Also examined were moderating effects of trait aggressiveness, trait altruistic helping, and trait egoistic helping. Prosocial games reduced state hostility and increased positive state affect. Violent video games had the opposite effects. These effects were moderated by trait physical aggression. Altruistic participants reported relatively more positive affect and less state hostility. Egoistic participants reported relatively more aggravated and mean feelings. Aggr. Behav. 38:263271, 2012. (c) 2012 Wiley Periodicals, Inc.