The current study examined the main effects of hostile attributional bias (HAB) and negative emotional responding on a variety of aggressive behaviors in adults, including general aggression, physical aggression, relational aggression, and verbal aggression. Effects of both externalizing (anger) and internalizing (embarrassment/upset) negative emotions were considered. In addition, the moderating roles of gender and impulsivity on the effects of HAB and negative emotional responding were explored. Multilevel models were fitted to data from 2,749 adult twins aged 20–55 from the PennTwins cohort. HAB was positively associated with all four forms of aggression. There was also a significant interaction between impulsivity and HAB for general aggression. Specifically, the relationship between HAB and general aggression was only significant for individuals with average or above-average levels of impulsivity. Negative emotional responding was also found to predict all measures of aggression, although in different ways. Anger was positively associated with all forms of aggression, whereas embarrassment/upset predicted decreased levels of general, physical, and verbal aggression but increased levels of relational aggression. The associations between negative emotional responding and aggression were generally stronger for males than females. The current study provides evidence for the utility of HAB and negative emotional responding as predictors of adult aggression and further suggests that gender and impulsivity may moderate their links with aggression. Aggr. Behav. 38:47-63, 2012. © 2011 Wiley Periodicals, Inc.