Individual differences in personality traits such as impulsivity and trait anger as well as environmental variables have an impact on aggressiveness. We tested a model incorporating the related variables of impulsiveness, trait anger, and aggression and incorporated the possible mediating influences of leisure-time activities. Regression analyses of data from 1129 pre-adolescents and 1093 adolescents (55.4% females) from a study evaluating the Spanish version of the Buss and Perry aggression questionnaire (AQ: Santisteban, Alvarado, & Recio, 2007) showed a relation between impulsiveness (Barratt Impulsiveness Scale) and aggression (AQ). Trait anger (Spielberger's State-Trait Anger Expression Inventory), the time spent watching TV and playing video games, and the time spent doing homework (all related to impulsiveness) also are related to physical, as well as verbal aggression (with low to moderate coefficients). Multiple mediation analyses confirm that media violence exposure and homework, respectively, can have aggravating and attenuating effects on self-reported aggression. These results provide key variables for longitudinal studies which could reveal the causal nature of the results found with our cross-sectional design. (C) 2008 Elsevier Ltd. All rights reserved.