The findings suggest that the relationships between prosocial behavior and physical aggression are complex and that prosocial behavior should not be viewed as a unitary construct. When the six types of prosocial behaviors were examined, only two had significant and negative links with physical aggression: altruism and compliant prosocial behaviors. This finding is consistent with the notion that altruistic acts are motivated by a prosocial personality or internalized values in addition to sympathy, such that altruistic acts may proceed from obligation rather than a deeply felt concern for the needs of others, which is the most powerful deterrent for physical aggression. Also, compliant prosocial behavior may stem from a desire to meet the expectations of others in order to be accepted. Thus prosocial behavior that does not stem from a genuine sympathy for people in need does not preclude physical aggression. Sympathy fully mediated the relations between compliant prosocial behavior and physical aggression, and partially mediated the relations between altruism and physical aggression and public prosocial behaviors and physical aggression. The 252 college students (68 men and 184 women) were recruited from a subject pool at a Pacific-coast State university. Students completed the empathic concerns and perspective-taking subscales from the Interpersonal Reactivity Index. They also completed the Prosocial Tendencies Measure. In order to assess both trait and state physical aggression, participants completed the Suppression of Aggression subscale of the Weinberger Adjustment Inventory. 2 tables, 3 figures, and 77 references