The aim of this study was to examine the relationship between self-esteem, narcissism, and measures of proactive and reactive aggression in two large community samples of young adults from two countries (the United Kingdom and Malaysia). Self-esteem and narcissism were measured through the Multidimensional Self-Esteem Inventory and the Narcissistic Personality Inventory, whereas aggression was measured by the Reactive–Proactive Aggression Questionnaire in 501 young adults with approximately equal numbers of men and women. In both countries, low levels of self-esteem were associated with reactive aggression while high levels of narcissism were associated with proactive aggression. Although this pattern was similar for both genders, the associations between both types of self-evaluation and proactive aggression were greater for men. The results suggest that people with low self-esteem are prone to greater reactive aggression due to anger and hostility, whereas those with high levels of narcissism can act with deliberate, planned aggression to achieve a goal. These effects appear stable across gender and culture.