This study investigated the effects of video game play on aggression. Using the General Aggression Model, as applied to video games by Anderson and Bushman,  this study measured physiological arousal, state hostility, and how aggressively participants would respond to three hypothetical scenarios. In addition, this study measured each of these variables multiple times to gauge how aggression would change with increased video game play. Results showed a significant increase from baseline in hostility and aggression (based on two of the three story stems), which is consistent with the General Aggression Model. This study adds to the existing literature on video games and aggression by showing that increased play of a violent first person shooter video game can significantly increase aggression from baseline. Aggr. Behav. 33:486–497, 2007. © 2007 Wiley-Liss, Inc.