In this review we examined effects of situational and personality factors of empathy upon aggressive behavior. Empathy was defined as consisting of cognitive (perspective-taking) and affective components (sympathy). It was hypothesized that these two components are evoked independently of each other. Understanding of other's suffering does not always lead to sympathy, but may sometimes lead to sadistic reactions. A number of studies were reviewed in which empathy was situationally aroused by exposure to pain cues, perceived similarity, and self-diclosure by a victim. The effects of these factors upon aggression were not consistent. For example, pain cues reduced aggression in nonangered subjects while sometimes escalated aggression in angered subjects. These results suggest that pain cues, similarity, and self-disclosure facilitate perspective-taking but do not determine emotional responses. What determines emotional reactions is the type of motives involved in aggressive behaivor. When an aggressor is motivated by hostile motives (the goal is to harm a victim), the situationally enhanced perspective taking is likely to lead more aggression. When he/she is motivated by nonhostile motives (the goal is other than to harm the victim), however, the enhanced perspective taking is likely to lead less aggression. Lastly, empathy as a personality trait was proposed as being differentially responsive to empathy-arousing stimuli, emphasizing the interaction effects upon aggression of personality and situational factors in arousal of empathy.