This study examined whether a combination of anger, hostility, and irrational beliefs, i.e., intolerance of rules frustration, intolerance of work frustration, demands for fairness, and self-downing would predict physical, verbal, and indirect aggression and peer ratings of aggression. Follow-up analysis tested gender as a moderator of the relations between irrational beliefs and aggression, and anger and aggression. One hundred thirty-five high school-aged adolescents completed measures of irrational beliefs, anger, hostility, and aggression. Results demonstrated that gender, anger, and an irrational belief of intolerance of rules frustration predicted physical aggression, while anger and irrational belief of intolerance of rules frustration uniquely predicted indirect aggression. Anger alone predicted verbal aggression. Males were more likely to report higher rate of physical aggression and were voted to be more aggressive by their peers. However, gender did not moderate the relations between cognition and aggression, and anger and aggression. Treatment and research implications are discussed.