Sadism is a "dark" trait that involves the experience of pleasure from others' pain, yet much is unknown about its link to aggression. Across eight studies (total = 2,255), sadism predicted greater aggression against both innocent targets and provocateurs. These associations occurred above-and-beyond general aggressiveness, impulsivity, and other "dark" traits. Sadism was associated with greater positive affect during aggression, which accounted for much of the variance in the sadism-aggression link. This aggressive pleasure was contingent on sadists' perceptions that their target suffered due to their aggressive act. After aggression, sadism was associated with increases in negative affect. Sadism thus appears to be a potent predictor of aggression that is motivated by the pleasure of causing pain. Such sadistic aggression ultimately backfires, resulting in greater negative affect. More generally, our results support the crucial role of anticipated and positive forms of affect in motivating aggression.