The aim of the present study was to examine whether there is a relation between a negative/aggressive interpretation bias, different types of aggression, and callous-unemotional traits in (delinquent) juveniles. We examined this research question in 2 different studies. The first study examines the relationship between a social negative interpretation bias with different types of aggression and callous-unemotional traits in 42 juvenile delinquent boys from a Juridical Youth Institution Centre and 29 healthy juvenile controls from a local high school in the Netherlands. Results showed that a negative interpretation bias was related to callous-unemotional traits, but specifically within the delinquent group. In the second study we examined this research question in more detail, using 3 different groups and two different measurements of a negative and aggressive interpretation bias (i.e., explicit vs. implicit measurement, respectively). This second study included 88 male participants ranging from 13 to 25 years. Subjects were now recruited from a local high school (healthy controls), an education project (at risk group) and from a Juridical Youth Institution (juvenile group). In the three different groups, there emerged different meaningful correlates. While in the healthy control group there were no significant correlates of a negative interpretation bias, for the two other groups some meaningful correlates were found. Within the at risk group, an aggressive interpretation bias was related to reactive aggression. Within the delinquent group, a negative interpretation bias was significantly related to reactive aggression, while an aggressive interpretation bias was significantly related to proactive aggression. So over the two studies, specifically within the delinquent groups, a negative interpretation bias seems positively related to aggression and callous-unemotional traits. These findings might indicate that the tendency to make negative or aggressive interpretations of potential innocuous situations might form an important mechanism underlying the relation between aggressive acts and the presence of elevated aggression and callous unemotional traits.