Youths with conduct disorders (CD) are particularly studied for their violent and aggressive behaviors. Many researchers considered aggressive behaviors as being either reactive or proactive. Moreover, factors such as age of CD onset, impulsivity, and callous-unemotional traits, separately, have been related to these different types of aggressive behaviors. However, very few studies addressed the combined contribution of these three factors on proactive and reactive aggression. This question was tested in a sample composed of 43 male adolescents with CD. A single regression analysis including all predictors and outcomes, using Bayesian statistics, was computed. Results indicated that impulsivity was related to reactive aggression, while CU traits were related to proactive aggression. These results suggest first, an important heterogeneity among youth with CD, probably leading to different trajectories and, second, that youths with callous-unemotional traits should receive special attention and care as they are more at risk for proactive aggression.