We assessed the role of trait anger and anger expression style on competitive/aggressive decision making and responding. In a 100‐trial iterated Prisoner’s Dilemma (IPD), with instructions to simulate wartime interactions, competition/aggression was defined as “attacking the opponent,” and “waiting for troop reinforcements” was the noncompetitive alternative response. Prior to play, 92 university student players completed the State‐Trait Anger Expression Inventory. They were then paired to play the IPD against partners of similar or dissimilar trait anger levels. At postplay, the State Anger scale was readministered. Results showed significant preplay to postplay increases in state anger, with greater increases shown by high trait anger players. Thus, high trait anger players were especially subject to arousal. Players in the high trait anger group made more competitive/attack responses, and they were more likely to do so when paired with a high trait anger partner. As a result of the high level of competitive/aggressive play, both groups ended with a negative troop count. Trait anger as a general personality temperament was predictive of state anger, competitive/attack responses, and the number of trials before a retaliation was made. The expressive style of anger‐control was also related to manner of play. Trait anger had strong direct and indirect effects through anger control on the number of competitive attack responses. It was concluded that trait anger, especially trait anger/temperament, and anger control difficulties may be toxic personality factors in decision making and competitive behavior. Aggr. Behav. 28:117–125, 2002. � 2002 Wiley‐Liss, Inc.