The principal aim was to analyze the relationship between aggressive behaviour in youth with intellectual disability and their perception of aggression. The group of 203 students with mild intellectual disability, aged 15-19 years old, took part in the study. A two-staged analysis was used, the first stage using the KJZA (Evident Aggressive Behaviour Questionnaire) to differentiate two groups: students with high level of aggressive behaviour (A) and students presenting low level of aggression (NA). For the second stage was used the Perception of Aggression Interview Questionnaire. Perception of aggression was analyzed as (a) knowledge of the term and (b) aggressive behaviour reasons; (c) opinion on aggression effectiveness; (d) relations with aggressive people; (e) knowledge about reducing aggression strategies. Aggressive students present more knowledge about aggression than their nonaggressive peers. Their opinions are less stereotypical, with high level of acceptance, without simplifying estimating of aggression. Generally students, also aggressive students, declare that aggression is not effective. They know various ways of reducing aggression. Results are discussed. It is necessary to create possibility to practice techniques for reducing aggression, nonaggressive reactions in different situations, to exposure nonaggressive models, to help in better understanding non only aggressive person but also her/his victim.