Sleep quality is a critical component of successful human functioning. Poor sleep quality is associated with aggressive behavior, yet the psychological mechanisms that drive this effect are incompletely understood. We tested the prediction that the association between poor sleep quality and aggression would be explained, in part, by a magnified experience of positive affect during aggression. We conducted 2 cross-sectional studies (Study 1, N = 388; Study 2, N = 317) and a third preregistered study (N = 379), which tested for mediation across 2 waves that were separated by 14-42 days. Across all 3 studies, we replicated the positive association between poor sleep quality and aggression. However, we did not observe compelling or consistent evidence that poor sleep quality is linked to greater positive affect during aggression. Such aggressive pleasure was temporally stable and predicted subsequent increases in aggressive behavior. These findings support a reinforcement model of aggressive affect, in which the pleasure of aggression promotes greater aggression over time-perhaps explaining why some individuals are more dispositionally aggressive than others. (PsycInfo Database Record (c) 2020 APA, all rights reserved).